US2294501A - Method for operating vapor generators - Google Patents

Description

. 1, 1942. R. D. JUNKINS METHOD FOR OPERATING VAPOR GENERKIORS Original Filed July 10, 1936 3 Sheets-Sheet l [roman/252 INVENTOR S e #4 E f m M 0 f. w M s a Sept. 1, 1942. R. D. JUNKINS 2,294,501

METHOD FOR OPERATING VAPOR GENERATORS 7 Original Filed July 10, 1936 3 Sheets-Sheet 2 T- [COMM/26E L7 6 n mw Wax/ Arse r Morse Gavtenmvc Star/01v 75 Wvsr:

INVENTOR Sept. 1942- R. D. JUNKINS 2,294,501

METHOD FOR- OPERATiNG VAPOR GENERATORS Original Filed July 10, 1936 3 Sheets-Sheet 5 6 Smzgzmvrre GA'IVEEAT/IVG 850770 INVENTOR Patented Sept. 1, 1942 Ms'rnon NT OFFICE Raymond D. Junkins, Cleveland, Ohio, assignor. to Bailey Meter Company, a corporation of Del- Original application M 10, 1938, Serial No. 89,916. Divided and this application June 20, 1939, Serial No. 280,136

2 Claims. (01. 123-1) This invention relates to the operation of heat exchangers and particularly of evaporators and vapor generators having'small liquid storage and a high rate of evaporation. In vapor generators there is always the problem of taking care of the solids carried by the feed liquid, unless con-. densate is used or extensive and expensive means are adapted totreat the feed liquid to precipitate the solids priorto the entrance of the liquid into the boiler, or the provision of treatment such that the solids will be carried in suspension to a collection chamber within the boiler, rather than allowing the solids to collect on the interior of the tubes with consequent hard scale formation and blistering. J

Prior boiler designs having large liquid storage and operating at a relatively low pressure, temperature, and rate of evaporation were provided with one or more mud drums, .or chambers, wherein solids could drop out of suspension or solution, due to the relative quiescence of the liquid at that zone. Even with such construction it was necessary to periodically blow down the boiler to remove the sludge, and such blowdown while serving the purpose of keeping the concentration of the boiler water below a predetermined maximum, at the same time resulted in a material loss of fiuid and of the heat which had been put into it. In certain constructions the boiler blowdown is passed through heat exchangers for recovery of the heat which had been put into the liquid, but such equipment entails a material capital investment.

With the modern vapor generator having small liquid storage and, a high rate of evaporation, there is relatively no quiescent zone wherein solids in suspension may drop out of the liquid,

and furthermore the vaporization zone wherein the vapor leaves the liquid body is not of material cross-section such as in a drum, but may be directly'in the tubes of relatively minute crosssectional area. It is known that in such construction and operation the greatest concentration of solids in the liquid and the greatest tendency for accumulation of sludge and scale upon the interior of thetube surfaces is at the vaporization zone and usually this is in a location relative to the heating such that a high temperature is experienced. Such a combination of precipitation of solids on a relatively small area in highly concentrated form and subjected to high temperature results in the formation of hard scale with either a restriction to flow within the tube passages or a blistering and burning of the tubes.

the drumless forced flow type of vapor. generator having a fluid flow path including one or more long small bore tubes, in which the flow in the path is initiated by the entrance of liquid under pressure at one end, and the exit of vapor only at the other end. Such a vapor generator having small liquid storage and operated with wide range combustion devices forms a combination rendering practical extremely high heat release rates with the consequent ability to economically handle practically instantaneous load changes from minimum to maximum, and vice versa, without heavy standby expense, and is particularly'suitable for operating conditions such as locomotive service, where load variations are of a wide range and are required to be met substantially instantaneously.

Such a vapor generator capable of vaporizing enormous quantities of liquid and having a very small liquid storage capacity quickly builds up the concentration of solids, or impurities, in the stored liquid unless provision is made for periodically or continuously discharging a part of the highly concentrated liquid, and thus reducing the concentration of the liquid. Here again arises the necessity of losing the heat within the blown down liquid, or going to the expense of elaborate heat exchange apparatus.

One form of forced circulation vapor generator has a heat absorbing surface or flow path for the working medium comprised of one or more long small bore tubes with an enlargement,

preferably at the end of the generating section, which acts as a separator to divide liquid and vapor. The vapor is then passed through a superheater while the excess liquid, carried through the tubes for the purpose of wetness and preventing scale deposit, is diverted out of the separator under regulated conditions. Such a separator type of boiler may be operated with, for example, five to ten per cent greater liquid inflow than vapor outflow, the excess water providing for tube wetness and to carry into the separator all of the scale forming materialswhich would otherwise continuously increase the concerglration of the liquid body within the flow pa This excess of liquid, carrying a considerable concentration of sludge or scale forming mate- .rials, passing continuously into the separator may be blown down continuously or under regulated manner, as is the concentrated liquid of the larger drum type of boiler. However, here Such difliculties are particularly prevalent in 68 again the pro em of w t n he heat in such blowdown liquid, or providing heat exchange apparatus, is encountered.

It has been proposed that the spillover from such a separator drum be allowed to continually pass to waste. Another proposal is that such spillover be in small proportion continuously bled to waste and the remainder introduced at the entrance to the flow passage and thus recirculated. Such an arrangement provides for a gradual building up of concentration within the flow path unless a material percentage is continuously bled to waste. The advantage lies in the fact that the generating surface will be continuously wetted so that even though there is some scale deposit it will not be allowed to bake, as would be the case were the interior of the tube subjected to relatively dry vapor rather than the wetting liquid. However, the liquid within the flow path would continue to build up as to concentration value.

A further proposal has been that the recirculated liquid be reintroduced at some intermediate point in the flow passage, but here again the concentration in a certain section of the flow path will continuously increase unless a material portion (percentage of the vapor outflow) is allowed to continuously go to waste.

A still further proposal has been that heat exchange apparatus be introduced to reclaim the heat of all of the spillover sent to waste. This is, of course, similar in principle regardless of the type of vapor generator or evaporator.

By the present invention I provide that, regardless of the type of vapor generator, the blowdown liquid containing a maximum concentration be evaporated completely in a separate evaporator, or as in the case of the forced flow vapor generator be evaporated to dryness in a separate heated flow path which may be so located and so constructed as to be readily cleaned or replaced.

Additionally the invention, regardless of the type of vapor generator, contemplates a continuous diversion of highly concentrated liquid, or blowdown, regulated in amount from certain variables in the boiler operation, such for example as the rate of vapor outflow or demand upon the generator, and additionally dependent upon a measure of the concentration or conductivity of the liquid in a certain location of the vapor generator, such for example as the vaporization drum or mud drum of a large storage boiler, or the separator of a once-through forced circulation boiler.

While I am aware that apparatus has been developed and utilized for determining the concentration and conductivity of boiler water, that the blowdown has been controlled from a measure of the conductivity of the boiler water, and furthermore in accordance with the rate of liquid inflow to the vapor generator, 'there has never, so far as I have been able to determine, been proposed a method of operation wherein the actual demand upon the vapor generator as indicated by the rate of vapor outflow is utilized either alone or in conjunction with a determination of conductivity to control the rate of divergence of highly concentrated liquid from the vapor generator regardless of whether such liquid is passed to waste directly, through heat exchangers, or as in accordance with the present invention, through a separate evaporator or evaporating section within the vapor generator.

A principal object of the present invention is to provide that all of the blowdown from any type of evaporator or vapor generator be passed through an evaporator or evaporating section and evaporated to dryness or to substantial dryness.

A still further object is to provide for the removal of solids from a vapor generator without loss of the heat contained in the carrier liquid.

A still further object is that in accordance with the present invention, and referring particularly to a forced flow type of vapor generator, a greater excess of liquid may be admitted relative to the vapor outflow for the purpose of tube wetness and the carrying through of scale forming materials without a consequent heat loss.

Another object is the provision of a control system wherein the amount of diverted liquid from the flow path or blowdown from an evaporator is controlled either alone from a measure of demand upon the generator, or in combination 'with an indication of conductivity, or of the concentration of the liquid.

I have chosen to illustrate and will describe my invention in connection with various types of vapor generators adapted to produce steam from water and showing the adaptability of'the invention to vapor generators which may have a large liquid storage space with a relatively low operating pressure, temperature, and rate of evaporation, as well as in connection with vapor generators having a very small liquid storage space and a very high rate of evaporation.

In the drawings:

Fig. 1 diagrammatically illustrates a drumless forced flow vapor generator to which the present invention is directed.

Fig. 2 illustrates in diagrammatic fashion a drumless forced flow vapor generator, such as Fig. 1, including a separate section in which the blowdown is evaporated.

Figs. 3 and 4 are enlarged details of a part of Fig. 2.

Fig. 5 illustrates a further embodiment of my invention applied to a forced circulation vapor generator.

In the various drawings identical parts bear the same reference numerals.

The drumless forced flow vapor generator to which the present invention is directed is diagrammatically illustrated in Fig. 1 to illustrate the fluid flow path as a single sinuous tube, to the economizer section I of which liquid is supplied under pressure through a conduit 2 from any source (not shown) under the control of a diaphragm actuated regulating valve 3. From the economizer section the fluid passes to and through the generating section 4, discharging into a separator 5. From the separator, vapor passes to and through the superheater 6, leaving by the conduit 1 to any vapor consuming apparatus. Products of combustion pass successively through the generating section, superheater and economizer, and may contact a part or all of the separator.

A burner 8 is supplied with fuel, such as oil, through a pipe 9 and with air to support combustion through a duct III. A control of the supply of the elements of combustion forms no part of the present invention.

ll represents means responsive to liquid level within the separator 5 and constitutes a. pressure casing enclosing a mercury U-tube connected across the vertical elevation of the separator. A float is adapted to rise and fall with the surface of the mercury in one leg and to thus cause a positioning of a pointer I2 relative to an index l3 to advise the instantaneous value of liquid level within the separator, and at the same time to position the pilot stem l4 of a pilot valve l5 eflfective in positioning the liquid inflow regulating valve 3. Thus the rate of liquid inflow to the vapor generator is continuously controlled in accordance with liquid level within the separator 5.

A rate of flow meter I6 is provided for continuously determining the demand upon the vapor generator as'indicated by the rate of vapor outflow. Such a meter is of a known type as disclosed in the patent to Ledoux 1,064,748, and is a differential pressure responsive device adapted to correct for non-linear relation between differential pressure and rate of flow, to the end that angular positioning of a pointer relative to an index I3 is by increments directly proportional to increments of rate of flow. I illustrate by dotted line within the flow meter I6 the outline of the internal construction wherein is a liquid sealed bell having walls of material thickness and shaped as described and claimed in said patent. The meter is further adapted to position a pilot stem I9 relative to a pilot casing 20 for establishing a loading pressure representative of rate of vapor outflow.

Pilots l5 and 20 are of a type forming the subject matter of a copending application of Clarence Johnson, Serial No. 673,212, filed May 27, 1933 and which issued Sept. 15, 1936, as Patent 2,054,464. Air under pressure is supplied to the interior of the pilot casings I5, 20 intermediate lands on the stems l4, l9. A fluid pressure in definite relation to axial movement of the stems |4, I9 is made available at the exit of the casings I5, 20. I indicate pipes or capillaries for transmitting such air loading pressures by dash lines to distinguish from other pipes or conduits. 1 indicate by small arrows at the side of the pilot casings I5, 20 an available supply of compressed air from any source and at a relatively low pressure, as for example 50 lbs. per square inch gage.

The separator 5 is provided with a liquid discharge pipe -2| having a control valve 22 therein for regulating the blowoff or drainage of liquid inflow valve 3A is illustrated as of a hand actuated type. or it may be regulated from any desired variable or factor.

Particular features of my invention as depicted in this figure relate to the disposal of the liquid drained from the separator 5 through the pipe 2|. It is to be understood that in this type of vapor generator approximately 10% more liquid is admitted through the conduit 2 than leaves as vapor through the conduit I. The excess liquid passing with the steam from the generating section 4 into the separator 5 builds up a pool of liquid within the separator to a predetermined liquid level. Thereafter there is a continuous bleed or drainage of liquid from the separator through the pipe 2| and I have herein illustrated the control of such drainage and the disposal of same.

The pipe 2| leads to a pump 30, discharging to a conduit 3| through a diaphragm actuated regulating valve 32 and a shutoff valve 33. The conduit 3| leads to a tube section 34, discharging through a valve 35 to the separator 5.

The tube section 34 may be formed as a hairpin turn, a sinuous shape, a spiral, or in other manner to conform to the general construction. I illustrate at Fig. 3 and Fig. 4. constructions which may be utilized, projecting inwardly through the refractory lining 36 and the steel outer casing 31 of the vapor generator, and provided for ready removal through disconnection of the v flanges 33.

It is contemplated that the pump 3|! will accomplish a forced circulation of liquid from the separator 5 through the section 34, wherein the liquid willbe vaporized. The flow through the section 34 being under the control of the regulating valve 32, in turn positioned responsive to from the separator to waste or as may be desired.

I illustrate a conductivity cell 23 located near the bottom of the separator 5, sensitive to conductivity of the liquid therein, and adapted to actuate a concentration meter 24. A pointer 25 is adapted to indicate, relative to an index 23, the value of concentration within the separator 5 and simultaneously to position a pilot stem 21 relative to the pilot case 23.

A fluid pressure representative of the instantaneous value of rate of vapor outflow and a fluid pressure representative of the value of concentration within the separator 5 are separately applied to an averaging relay 29. The latter is efiective to establish a fluid pressure adapted to position the regulating valve 22. Certain features of the relay 29 are disclosed and claimed in the copending application, Serial No. 8023, of Paul S. Dickey, filed in the United States Patent Oflice February 25, 1935, and which. issued as Patent 2,098,913 on Nov. 9, 1937.

From the above description it will be apparent that the control of liquid outflow through the pipe 2| is Jointly from rate of vapor outflow from the vapor generator and from value of concentration of the liquid within the separator 5.

Referring now in particular to Fig. 2, I show therein a forced circulation vapor generator similar to that of Fig. 1. Here, however, the liquid rate of vapor outflow and to liquid level within the separator 5.

The actual size and proportion of the section v 34 will depend upon the total capacity of the vapor generator, the actual rate of flow of liquid through the conduit 3|under normal operation, and theflocation of the section 34 within the heated gaspassage. The location relative to the heating is preferably such, as is the proportion of length and size of tubing, that all of the liquid passing through the conduit 3| into the section 34 will be vaporized and vapor only will pass througkthevalve 35 to the separator 5. Thus under normal conditions of operation, the liquid leaving the generating section 4 and passing to the separator 5 willcarry with it all of the solids originally possessed by the liquid inflow, and the excess liquid and solids passing through the conduit 2| will enter the section 34 where the liquid will be vaporized, thus-leaving all of the solids in the section. If, however, under certain operating conditions there is more liquid passing through the conduit 3| than may be evaporated in the section 34, the excess liquid along with the vapor generated will pass into the separator 5 and recirculate through the conduit 2| so that no difllculty'will be encountered. However, as the rating on the complete unit goes up and thus the total quantity of liquid passing through the conduit 3| increases, at the same time the heating effective upon thesection 34 will increase and thus increase its vaporizing capacity. It is thus expected that at no time will there be any material amount of liquid passing from the section 34 to the separator 5.

It will be observed that the section 34 primarily serves the purpose of collecting all of the solids in the liquid of the separator 5, conserving all of the heat of said liquid, and vaporizing all of said liquid at a pressure and temperature condition such that it may co-mingle with the vapor of the separator 5 to pass to the superheater 8.

The valve 32 is under the joint control of. the meters I6 and therefore is positioned responsive not only to the rate of vapor outflow, but also to the liquid level within the separator 5.

The conductivity cell 23, so located as to measure the concentration of the liquid within the separator 5, produces an indication upon the index 26 of the concentration and furthermore controls the positioning of a regulating valve 39. The valve 39 is so adjusted as to normally regulate the discharge of only a very small portion of liquid from the separator 5 to waste. Under ideal conditions of operation there may be no flow whatever through the valve 39 to waste.

The vaporizing section 34 may be removed for cleaning or replacement whether or not the generator is in operation, by closing valves 33, 35, disconnecting flanges 38, and allowing the regulating valve 39 and hand valve 42 to take care of liquid within the separator 5.

I have illustrated provisions for washing out the section 34, while the vapor generator 'is in operation. By closing valves 33 and 35 and opening valves 40 and 4|, the flow of liquid from the separator 5 to the section 34 is stopped and a flow of wash water is passed through the section 34 in opposite direction to normal flowand to waste.

'While such washing or cleaning operation is being accomplished the hand valve 42 may be opened to take care of the excess. water which reaches the separator 5.

In Fig. 5 I illustrate an arrangement wherein the rate of liquid inflow is continuously controlled by means of the regulating valve 3 from level within the separator 5. The rate of blowdown of liquid from the separator 5 is controlled by the positioning of the valve 22 jointly from rate of vapor outflow, rate of blowdown flow, and conductivity or concentration within the separator 5.

The rate of flow meter l8 positions a vertically suspended link |9A in accordance with rate of vapor outflow. A rate of flow meter I8 positions an indicator 19 and a vertically suspended link 80 in accordance with rate of flow of the blowdown through the conduit 2|. The suspended links |9A, 80 are pivotally connected to opposite ends of a floating link 8|, from an intermediate point of which is freely suspended a vertical link 82.

The vertical link 21A is suspended from the indicator 25 and positioned in accordance with concentration within the separator 5. The lower end of the link 21A and of the link 82 are each pivotally connected to opposite ends of a floating member 83. Intermediate the ends of the member 83 is pivotally suspended a pilot stem 84 for the pilot valve 28. The pilot valve 28 establishes an air loading pressure for the regulating valve 22.

It will be observed then that normally a deflnite relation exists between the rate of vapor outflow and the rate of blowdown flow. 1!, however, concentration within the separator 5 departs from a desired value, the conductivity meter 24 will cause a readjustment positioning of the pilot valve 84 and correspondingly of the regulating valve 22 to satisfy that function. It will be noted that should conductivity within the separator 5 increase, the valve 22 will be opened to greater extent, and a corresponding greater flow of liquid from the separator will result. This lowering in level within the separator 5 will cause an increase in liquid supply to the vapor generator to restore the level to normal, and by thus increasing the fresh liquid within the system the relatively highly concentrated liquid within the separator 5 will be diluted with a lowering of the entire concentration in the system.

While I have illustrated and described certain preferred embodiments of my invention it is, of course, understood that there may be other modes and apparatus for carrying out the invention and that I am to be limited only as to the claims in view of prior art.

In general, the blowdown from any evaporator or container wherein a liquid may increase in concentration, is passed to a separate evaporator section where the said liquid is preferably evaporated to dryness, thus dropping out the solids or scale producing material in a location which may be readily replaced or cleaned. Furthermore, I employ a measure of conductivity to determine the concentration and control the blowdown therefrom.

This application is a division of the parent Serial No. 89,916, filed July 10, 1936, and which has issued as Patent 2,170,351 on August 22, 1939.

What I claim as new, and desire to secure by Letters Patent of the United States, is:

1. The method of operating a vapor generator which includes supplying liquid to the vapor generator at a rate continuously in excess of the rate of vapor generated, continuously diverting the excess liquid from the vapor generator adjacent the division zone between liquid and vapor, maintaining the division zone at a predetermined location through regulation ofliquid inflow, determining the concentration of the liquid adjacent the division zone, measuring vapor outflow, and regulating the diversion conjointly from the determination of concentration and the measure of vapor outflow.

2. The method of operating a vapor generator which includes, continuously diverting liquid from adjacent the vaporization zone between liquid and vapor in the vapor generator proportionate to rate of vapor outflow, modifying such diversion dependent upon amount of liquid in the vapor generator, and controlling additional diversion responsive to a determination of liquid concentration adjacent the vaporization zone.

RAYMOND D. J UNmNS.

Images