US2170351A - Method of operating vapor generators - Google Patents

Description

8- R. D. JUNKINS I 2,170,351

METHOD OF OPERATING VAPOR GENERATORS Filed July 10, 1956 2 SheetseShe-et 1 Sa-mwarae FIG.1 a m f INVENTOR Au 22, 1939. R. D. JUNKINS 2,170,351

METHOD OF OPERATING VAPOR GENERATORS Filed July 10, 1936 2 Sheets-Sheet 2 76 Mars Eamon/25E SUPEBHEA FEE Patented Aug. 22, 1939 men or ornnn'rme varon eunnna'rons Raymond J assigrior to tion of Delaware T OFFICE ls, @leveland Heights, (lliio, Bailey Meter tlonipany, a corpora- Application July it, 19%, Serial No. M916 5 out,

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 5: there is always the problem of taking care of the solids carried by the feed liquid, unless condensate is used or extensive and expensive means are adapted to treat the feed liquid to precipitate the solids prior to 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.

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 oi 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 fluid 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 modem vapor generator having small 85 liquid storage and a high rate of evaporation,

there is relatively no quiescent zone wherein solids in suspension may dropout 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 sectional area. It is known that in such con.-

struction and operation the greatest concentration of solids in the liquid and the greatest tendency for accumulation of sludge and scale upon the interior of the tube 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 0! hard scale with either a. restriction to flow within the tube passages or a blistering and burning of the tubes.

Such difllculties are particularly prevalent in relatively minute cross (till. Mb-d) the drumless forced flow type of vapor generator having a fluid flow path long small bore tubes, path is initiated by including one or more in which the flow in the 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 devic ing practical extremely high es forms a combination renderheat release rates with the consequent ability to economically handle practically instantaneous load changes from minimum tomaximum, and vice versa,

without heavy standby expense, and is particularly suitable for operating conditions suchas 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 stor the concentration age capacity quickly builds up 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 necessity of losing liquid. Here again arises the heat within the blOWn the has a heat absorbing working medium small bore tubes with surface or flow path for the comprised of one or more long an enlargement, preferably atthe end of the generating section, which acts as a separator to divide liquid and vapor;

The vapor is then while the excess liquid,

passed through a superheater 35 carried through the tubes for the purpose of wetness and preventing scale deposit, is diverted out of the separator under regulated conditl boiler may be operated with, for example, to ten per cent greater Such a separator type of five 40 liquid inflow than vapor outflow, the excess water providing for tube wetness and to carry into the separator. all of the scale forming materials which would otherwise continuously increase liquid body within the This excess of concentration of how path. liquid, carrying a considerable sludge or scale forming materials, passing continuously into the separator may be blown down continuously or under regulated 5 manner, as is the concentrated liquid .of the of wastin of boiler. However, here again the heat in such blowdown liquid, or providing heat exchange apparatus, is encountered.

the concentration of the 45 I 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 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.

Another object is that such an evaporator or evaporating section be so constructed and located that it may readily be removed, cleaned, or replaced.

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 further embodiment of my invention.

In the 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 valve 3A. 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 01' the supply of the elements of combustion forms no part of the present invention.

ll represents means responsive to liquid level within the separator 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 l2 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 ll of a pilot valve I 5 effective in positioning the valve 32.

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 or 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 l'l relative to an index it is by increments directly proportional to increments of rate of flow. I illustrate by dotted line within the flow meter IS the outline of the internal construction wherein is a liquid sealed bell having walls of material thick ness and shaped as described and claimed in said patent. The meter is further adapted to position a pilot stem 43 relative to a pilot casing 20 for establishing a loading pressure representative 0! rate of vapor outflow.

' Pilots l5 and 20 are of a type forming the subject matter of the patent to Clarence Johnson, No. 2,054,464. Air under pressure is supplied to the interior of the pilot casings I5, 20 intermediate lands on the stems l4, IS. A fluid pressure in definite relation to axial movement of the stems I 4, I3 is made available at the exit of the casings I5, 20. I indicate pipes or capillarie's for transmitting such air loading presthe side of the pilot casings I 5, 20 an available supply of compressed air from any source and at a relatively low. pressure, as for example 50 lb. per square inch gage.

I illustrate a conductivity cell 23 located near the bottom of the'separator 5, sensitive to con- 7 ductivityof the liquid therein, and adapted to actuate a concentration meter 24. A pointer 25 is adapted to indicate, relative to an index 25, the value oi. concentration within the separator 5 and simultaneously to position a valve 33.

A fluid pressure representative of the instantaneous value of rate of vapor outflow and a fluid pressure representative of the level of liquid within the separator 5 are separately applied to an averaging relay 2!. The latter is efl'ective to establish a fluid pressure adapted to position the regulating valve 32. Certain features of the relay 23 are disclosed and claimed in the patent to Paul S. Dickey No. 2,098,913.

Particular features of my invention as depicted inthis flgure relate to the disposal bf 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 the generating section 4 as vapor. The excess liquid passing with the steam train 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 bleedondrainage of liquid from the separator through the pipe 2| and I have herein illustrated the control of such drainage and the disposal of same.

liquid will be vaporized. The flow through the section 34 being under the control of the regulating valve 32, in turn positioned responsive to rate of vapor outflow and to liquid level within the separator 5.

The actual size and proportion of the section 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 the location of the section 34 within the heated gas passage. 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 through the valve 35 to the separator 5. Thus under normal conditions of operation, the liquid leaving the generating section 4 and passing to the separator 5 will carry 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 dimculty will be encountered. However, as the rating on the complete unit goes up and thus the total quantity 0! liquid passing through the conduit 3| increases, at the same time the heating effective upon the section 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 liquidof 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 6.

The valve 32 is under the joint control of the meters ll, l5 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 28 of the concentration and furthermore controls the positioning of a regulating valve 33. The valve 33 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 thr ugh the valve 33 to waste.

The vapor ng section 34 may be removed for cleaning or replacement whether or not the generator is in operation, by closing valves 33, 35, disconnecting flanges 33, and allowing the regulating valve 33 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 sep' arator 5 to the section 34' is stopped and a now of wash water is passed through the section 34 in opposite direction to normal flow and to waste. While such washing or cleaning operation is being accomplished the hand valve 42 may be opened to take care 01' the excess water which reaches the separator 5.

In Fig. 2 I illustrate in diagrammatic manner an arrangement in connection with a drumless forced flow vapor generator, wherein the liquid discharged from the separator 5 is continuously roughly proportioned to the rate of liquid inflow throughthe conduit 2. Furthermore that such discharged liquid passes through an external sep arately heated evaporator of a design which may be readily cleaned.

Liquid from the separator 5 passes through a conduit 2| to one cylinder compartment 43 of a reciprocating pump 44 driven by a motor 45. The motor is under the control of a rheostat 45, a movable contact of which is positioned by and with the indicator I! of the vapor outflow meter l6. Thus the liquid supply pump 44 is driven in accordance with the demand upon the vapor generator as indicated by the rate of vapor outflow. The general arrangement is that approximately 20% more liquid is supplied through the conduit 2 than leaves the generating section t-as vapor. In otherwords, one of the five cylinders of the pump 44 is supplying liquid to the conduit 2, which liquid will return through the conduit 2i and the cylinder 43. The liquid pumped by the remaining four cylinders of the pump 44 leaves the generating section 4 as vapor.

The flow of liquid through the conduit 2| from the separator 5 is further controlled by means of a valve 41 responsive to a float 48.

The liquid leaving the cylinder 43 passes through a conduit 49 to a superheated vapor evaporator 50 having hairpin tubes 5| connecting between compartments 52, 53. superheated vapor from the conduit 1 is admitted under the control of a valve 54 to the compartment 53 and thence through the hairpin tubes to the compartment 52 and the conduit 55 through which the now relatively cooler vapor passes to the separator 5.

ized thereby, the vapor leaving by the conduit 56 to the separator 5.

The heating or vaporizing capacity of the unit 50 depends to a great extent upon the amount of superheated vapor admitted through the valve 54. However, no difilculty will be encountered should the flow of such heating vapor be too great or too little for optimum conditions. If too great, then the vapor entering the separator through the conduit 55 will be somewhat hotter than the vapor and liquid in the. separator 5. If too little vapor is passed through the valve 54, then the vapor through the conduit 55 will be cooled and possibly even condensed to have some liquid. Neither condition will affect the operation, as the co-mingling of such fluid entering through the conduit 55 with the vapor and liquid within the separator 5 will be satisfactory. At the same time an excess of heat in the unit 50 will evaporate the liquid entering through the conduit 49 faster and to possibly a higher temperature, while a deficiency of heat may result in some liquid being carried over through the conduit 56 to the separator 5. Again no difliculty in operation will be encountered.

The primary object will be served in that the scale forming material will all be carried out of the sections l and 4 of the vapor generator by the excess liquid to the separator 5 and from there will be pumped to the evaporator 50 where the scale forming material will be deposited. Such an evaporator is, of course, adapted for ready removal of the tube bank for cleaning. The evaporator 50 may be removed from service for clean- The liquid entering the evaporator 50 by the conduit- 49 surrounds the heating tubes 5| and is vapor- 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.

Certain features of my invention, described and illustrated but not claimed herein, are disclosed and claimed in my copending divisional application Serial No. 280,136 filed in the United States Patent Oflice June 20, 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 passing vaporizable liquid through an economizer and vapor generating sections in excess of the vapor generated from the liquid in said sections, separating the excess liquid from the vapor in a separator, passing the vapor so separated through a superheater, and vaporizing the excess liquid in an auxiliary vapor generating section.

2. The method of operating a vapor generator which includes passing vaporizable liquid through an economizer and vapor generating sections in excess of the vapor generated from the liquid in said sections, separating the excess liquid from the vapor in a separator, passing the vapor so separated through a superheater, vaporizing the excess liquid in an auxiliary vapor gererating section, and returning the vapor generated in the auxiliary vapor generating section to the separator.

3. The method of operating a vapor generator of the forced flow type which includes, passing the liquid through an economizer and vapor generating sections, supplying liquid to the economizer and vapor generator sections in excess of the amount of vapor generated so that solids are carried inthe excess liquid and deposition of solids in the economizer and vapor generating sections is prevented, separating the excess liquid from the vapor in a separator, passing the vapor so separated through a superheater, vaporizing the excess liquid in an auxiliary vaporizing section so that the solids carried by the liquid will be deposited therein, and'returning the vapor generated in the auxiliary vaporizing section to the separator.

4. The method of operating a vapor generator of the forced flow type having an economizer section, a main vapor generating section, a superheating section, a liquid vapor separator between the vapor generating section and the superheating section, and an auxiliary vapor generating section'which includes, eflecting vaporization of less than all of the liquid which passes through the economizer and main generating section to prevent the deposition of solids therein, separating the vapor from the liquid in the separator,

passing the vapor so separated through the super.-

heating section, passing the liquid separated in the separator through the auxiliary vapor generating section, effecting complete vaporization of the liquid in the auxiliary vapor generating section so that solids will be deposited therein and returning the vapor generated in the auxiliary vapor generating section to the separator.

5. The method of operatinga vapor generator having an economizer section, a vapor generating section, a superheating section, and a liquid-vapor separator between the vapor generating and superheating sections'which includes, heating the vapor, generator so that more than 50% and less than 90% of the liquid'admitted to the economizer section is vaporized in the economizer and vapor generating sections, eiifecting separation of the liquid and vapor in the separator, passing the vapor through the superheating section, diverting the liquid separated from the vapor in the separator through an auxiliary vapor generating section so that substantially all of the liquid is vaporized, and returning the vapor so formed in the auxiliary vaporizing section to the vapor separator.

RAYMOND D. JUNKINS.

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