US3488474A

US3488474A - Electric steam generator

Info

Publication number: US3488474A
Application number: US676968A
Authority: US
Inventors: Fred Q Saunders
Original assignee: FRED Q SAUNDERS
Current assignee: FRED Q SAUNDERS
Priority date: 1967-10-20
Filing date: 1967-10-20
Publication date: 1970-01-06
Anticipated expiration: 1987-01-06

Description

1970 P. Q. SAUNDERS ELECTRIC STEAM GENERATOR '4 Sheets-Sheet 1 Filed Oct. 20, 1967 R o .2-.. .1..J m a??? s M L w m9 v a v v v63 fie da Jayne/er:

F. Q. SAUNDERS ELECTRIC STEAM GENERATOR Jan. 6, 1970 4 Sheets-Sheet- 2 Filed Oct. 20. 196'? INVENTOR flea! Q fauna/en ATTORNEY I Jan. 6, 1970 F. Q. SAUNDERS ELECTRIC STEAM GENERATOR 4 sheets-sheet a Md Oct. 20. 1957 vmvgsmon 5 Q- Jauaa'ers w Illllallllll llll l 131w fi. m W W w M a 1 7 n n p. w w w u w? w m 5 k Mm w WW Ww mm 3 M in. OWW v%w may M 8D I E50 UM NM [0 #m w a w m I m m Wm TM. m

ATTORNEY Jan. 6, 1970 F. Q. SAUNDERS I 3,488,474,

ELECTRIC STEAM GENERATOR Filed Oct. 20. 195'? 4 sneexsgsheep 4 :mvsmoa ATTORNEY United States Patent 3,488,474 ELECTRIC STEAM GENERATOR Fred Q. Saunders, 7622 Hollins Road,

Richmond, Va. 23229 Filed Oct. 20, 1967, Ser. No. 676,968 Int. Cl. Hb 3/60 US. Cl. 219-284 12 Claims ABSTRACT OF THE DISCLOSURE A boiler having an electrode immersed in current conductive water and a surge chamber connected to the boiler so that water may be transferred between the two vessels to control the extent of electrode immersion and electric load on the boiler as a function of sensing pressure drop across an obstruction in a steam outlet line of the boiler. Also, means responsive to water level variations in the boiler and to pressure drop variations in the steam outlet line are provided for controlling the conductivity of boiler water.

This invention relates to new and useful improvements in electric steam generators of the general type having a boiler with one or more electrodes immersed in current conductive water, and the principal object of the invention is to facilitate highly efficient operation of steam generators of this type so that the pressure of the generated steam and the electric load required for steam generation may be held within very close limits notwithstanding the steam load demand, and so that conductivity of water in the boiler may be coordinated with changes in water level and steam pressure differential across a partial obstruction in the steam outlet line at various predetermined electric loads of the boiler.

In operating electric steam generators of the aforementioned type it is desirable to maintain steam pressure at the outlet within close limits, say within 3% of a predetermined point. It is also desirable to maintain the electric load within close limits, say within 3% of a predetermined maximum, regardless of the steam load demand. Moreover, it is desirable to regulate steam pressure in relation to water level by closely controlling the conductivity of water under different, predetermined maximum electric loads of the boiler.

Briefly, the electric steam generator of the invention attains the desired requirements by the provision of highly efiicient and dependable control means which include the following: (a) means for sensing water level in the boiler and feeding water thereinto when the level is below normal; (b) means for sensing pressure of generated steam and utilizing this to adjust the water level in the boiler in accordance with the steam demand; (c) utilization of the water level adjustment to control the extent to which the electrode is immersed, thus controlling the electric load; and (d) means for coordinating sensing of the water level and generated steam flow for varying the conductivity of water under a predetermined load limit.

Other objects and features of the invention will become apparent from the following description taken in conjunction with the accompanying drawings, wherein like characters of reference are used to designate like parts, and wherein:

FIG. 1 is a diagrammatic illustration, partly in section, showing the electric steam generator of the invention with its associated controls;

FIG. 2 is a cross-sectional view of the boiler, taken substantially in the plane of the line 22 in FIG. 1;

FIG. 3 is a diagram, similar to that in FIG. 1 but showing a modified arrangement of the invention;

Patented Jan. 6, 1970 FIG. 4 is a wiring diagram of the electrical components used in the embodiment of either FIG. 1 or FIG. 3;

FIG. 5 is a diagrammatic illustration, partly in perspective and partly in section, showing a modified control; and

FIG. 6 is a chart showing relationship of water level and boiler load under proper control of water conductivity.

Referring now to the accompanying drawings in detail, particularly FIGS. 1 and 2 thereof, the general reference numeral 10 designates a boiler containing one or more vertically elongated electrodes 11 immersed in current conductive water 12, the maximum and minimum water levels 12a and 120 being at or adjacent the respective upper and lower ends of the electrodes. For illustrative purposes a set of three electrodes is shown in the drawings, the same being surrounded by an open-ended, vertically elongated grounding shield 13 of a cloverleaf crosssection, as will be apparent from FIG. 2. The bottom of the boiler has a water inlet 14, and a steam outlet line 15 extends from the top of the boiler to wherever generated steam is to be utilized. A suitable excess pressure relief valve 16 is provided on the boiler.

A vertically elongated surge chamber or tank 17 is disposed exteriorly of the boiler 10, the bottom of the surge chamber having a water inlet 18 connected, as is the inlet 14 of the boiler, to a water feed conduit 19, the normal water level in the surge chamber being substantially at the maximum water level 12a in the boiler. The top of the surge chamber 17 is provided with a pressure transmitting line 20 which is connected to the steam outlet line 15 and thus communicates the top of the boiler with the top of the surge chamber.

A branch line 21 extends from the pressure transmitting line 20 and two

vertical lines

22, 23 extend in parallel between this branch line and the water feed conduit 19. The line 22 is equipped with a sightglass type gauge 24 indicating the water level in the surge chamber 17, and the line 23 is provided with a water level sensing switch 25. The latter consists of a housing 26 having a probe 27 extending laterally thereinto, the probe being insulated from the housing. When the water level in the surge chamber 17 and housing 26 is at or above the level of the probe 27, an electric circuit is completed through the conductive water and through the probe, as hereinafter described. However, if the water level is below the probe, the electric circuit is open. A suitable vent 28 may also be provided on the branch line 21, as shown.

Similarly, a branch line 29.extends from the steam outlet line 15 and two

vertical lines

30, 31 extend in parallel between this branch line and the water feed conduit 19. The line 30 carries a sightglass type gauge 32 indicating water level in the boiler 10, and the line 31 carries a water level sensing switch 33. The latter is similar to the switch 25 but contains two probes 34, 35, one above the other. The upper probe 34 is disposed at the maximum water level 12a in the boiler and the lower probe 35 is at a somewhat lower level, for example where approximately of the length of the electrodes 11 is immersed in the water 12, The water feed conduit 19 is equipped with a manually operated drain valve 36 so that water may be drained from the boiler and surge chamber when so desired, after a manually operated water feed valve 37a on the conduit 19 has been closed. An electrically operated feed valve 37 is also provided on the conduit 19 upstream from the

lines

22, 23, and downstream from the manual valve 37a as shown.

The water in the system is made electrically conductive by dissolved chemicals present in the water introduced in the system and by addition of a suitable chemical contained in a chemical reservoir 38. The latter receives a supply of water through a line 39 connected to the water feed conduit 19 upstream from the valve 37, and the chemically treated, strongly concentrated water is passed from the reservoir 38 to the boiler through a chemical feed line 41 equipped with electrically operated valve 42. A Water blow-down line 43 extends from the line 41 and is provided with an electrically operated valve 44. Thus, if the conductivity of water in the boiler is to be increased, the blow-down valve 44 is closed and the chemical feed valve 42 is opened to allow more chemical to be introduced into the water in the boiler. On the other hand, when water conductivity is to be decreased, the valve 42 is closed and the blow-down valve 44 is opened, thus permitting a certain amount of chemically treated water to be drained from the boiler and replaced by untreated water from the feed conduit 19, whereby the chemical concentration of the water in the boiler is diluted.

For purposes hereinafter described, the pressure transmitting line 20 between the boiler and the surge chamber is provided with an electrically operated throttling valve 45. The steam outlet line is equipped with obstruction means such as a manually adjustable valve 46 and/or an orifice 47, such obstruction means creating a pressure differential in the steam outlet line 15 upstream and downstream of the obstruction means, or in other words, a pressure drop across the obstruction means. This pressure differential is sensed by an electric switch 48 through

pressure sampling lines

49, 50 which are connected to the steam line 15 upstream and downstream of the obstruction means, as illustrated. The line 15 is also provided downstream from the valve 46 with a differential pressure control valve 51 for maintaining a constant set pressure difierential say at a reduction of in the line 15 downstream from the valve 51. The valve 51 may be actuated by a diaphragm type controller 51a having an upstream pressure sampling line 52 connected to the line 50, and a downstream pressure sampling line 53 connected to a pressure sampling line 54 of a main pressure control switch 55. A manually adjustable throttling valve 56 is provided for continuously bleeding steam from the line 20 and in turn surge chamber 17 to the line 15, as shown.

The purpose of using the combination pressure dilferential valve 51 and bleed valve 56 is to insure that the pressure in line 15 down stream from valve 51 is substantially less than the pressure in boiler chamber 10 at all times, and to insure a constant bleeding of steam from chamber 10 into the low pressure section of line 15 at all times that steam is being generated, Steam flow through valve 56 is relatively small compared to the volume which will pass through valve 45 when it is open. As valve 45 is throttled, flow through it reduces but the flow through valve 56 remains unchanged. As valve 45 approaches a totally closed position, valve 56 continues to bleed steam from line 20 and in turn surge tank 17 at a substantially constant rate of flow thus providing a positive means of assuring a pressure dilTerential between boiler chamber 10 and surge chamber 17, and in turn a positive displacement of water in boiler 10 when the pressure limit is reached as sensed by control 55 or when the maximum load limit is approached as sensed by control 48. It can be readily observed that by using this principle of operation, surge chamber 17 may be located at an elevation substantially higher than that of boiler 10. Sur-ge chamber 17 may be mounted above boiler 10 if desired so long as the pressure differential maintained by valve 51 is sufiicient to force water from boiler 10 into surge chamber 17 at the desired velocity. In the event surge chamber 17 is mounted at an elevation higher than that shown in FIG. 1, connecting line 18 is extended to the bottom of the raised surge chamber 17 and water level control remains at its present level (level 12a) with its top sampling line 21 extending to the top of surge chamber 17 (line 20 inlet to surge chamber 17).

A second suitable excess pressure relief valve 16a is provided to relieve pressure in line 15 downstream from pressure difierential valve 51. Relief pressure setting for relief valve 16a is lower than that of relief valve 16 by at least the differential pressure setting on valve 51.

Attention is now directed to FIG. 4 which shows the wiring diagram of the various electrical components. First, the water feed valve 37 in the conduit 19 is operated by a solenoid 57 receiving current through the contact 58 of a relay 59 which is energized when the water level in the surge chamber 17 and in the housing 26 of the water level sensing switch 25 is at or above the level of the probe 27, as already explained. The valve 37 is normally closed when the water level is at or above the probe 27, but is opened when the water level drops below the probe, so that more water may be fed into the system through the conduit 19. In this manner the water level in the boiler 10 and surge chamber 17 is normally maintained at the maximum level 12a, under which circumstances the electrodes 11 are fully immersed in the water in the boiler and are thus capable of operating to generate steam under maximum load demands,

The most effective method of quickly and positively changing the rate of steam generation is by changing the immersed length of the electrodes in the water in the boiler, which may be done by changing the water level in the boiler between the maximum 12a and the minimum 12c. When the throttling valve 45 in the pressure transmitting line 20 is fully open, the steam pressure in the top of the boiler is substantially the same as in the top of the surge chamber 17, and the water level in the two vessels is also substantially the same. However, as the valve 45 is throttled, the pressure in the surge chamber 17 will drop below that in the boiler and the higher pressure in the boiler will cause water to be transferred from the boiler into the surge chamber through the conduit 19, so that the water level in the boiler will be below that in the surge chamber and a correspondingly shorter length of the electrodes will remain immersed in the water in the boiler, until the minimum level 120 is reached, where the electrodes will not be immersed at all and steam generation will cease.

It will be apparent from the foregoing that by opening or closing the throttling valve 45, the water level in the boiler may be changed and the extent of electrode immersion thus controlled for between zero and maximum steam generation under a given load. The throttling valve 45 is operated by a solenoid 60 having parallel connections 61, 62 respectively to a contact 63 of the switch 55 and a contact 64 of the switch 48. The switch 55 includes a diaphragm actuator 65 for the contact 63, the actuator 65 responding to steam pressure in the outlet line 15 sensed through the sampling line 54. The switch 55 is manually set at a predetermined point, say p.s.i. of steam pressure in the line 15, and when this pressure is reached, the contact 63 of the switch closes to energize the solenoid or motor 60 of the throttling valve 45, which in turn causes lowering of the water-level in the boiler and a corresponding decrease in the rate of steam generation, thus preventing the steam pressure in the line 15 (at the sampling line 54) from exceeding the setting of the switch.

The valve 45 may also be throttled by closing of the contact 64 of the switch 48, this being a pressure differential switch operated by a diaphragm actuator 66 which has the

pressure sampling lines

49, 50 in communication with the opposite sides of the diaphragm. As the generated steam flows through the outlet line 15 past the manually set obstruction means 46 and/ or 47, a pressure drop across the obstruction means results in a higher pressure in the upstream sampling line 49 than in the downstream line 50, so that the actuator 66 causes the switch contact 64 to close at a predetermined set point. The pressure drop across the obstruction means 46 or 47 is a function of the rate of steam passing therethrough, and the rate of electric power consumption at the electrodes 11 is directly proportional to the rate at which steam is being generated. Thus, the pressure difierential switch 48 may be set to close the contact 64 when a predetermined maximum electric load is reached, whereby to lower the water level in the boiler and correspondingly reduce the electric power absorbing capacity of the electrodes so that the system is limited as to the amount of electric power which it can draw.

The kilowatt load at which the switch 48 becomes effective to limit the power consumed as mentioned above may be varied in a number of ways, as for example, by changing the spring adjustment of the switch actuator 66 to close the switch contact 66 at higher or lower differential of pressure, a higher pressure differential representing a greater steam flow and in turn a higher kilowatt load. If the constructing orifice 47 is fixed, the pressure drop across it will be proportionate to the steam flow through it. An increase or decrease in steam flow through the fixed orifice and, in turn, a change in pressure drop across it, may be compensated for by changing the setting of the switch 48 as to the pressure differential at which the switch closes.

The orifice 47 may be adjustable rather than fixed, in which event it would be an equivalent of the adjustable throttling valve 46 such as may be used either in substitution for or in addition to the orifice 47. In view of these possible alternatives, both the orifice 47 and the valve 46 have been shown in the drawings. By using an adjustable orifice 47, or the throttling valve 46, the adjustment of the switch 48 may remain at a set point while the orifice 47 or valve 46 are adjusted to provide the desired pressure differential thereacross. Thus, for example, if the switch 48 closes by a given flow of steam through the valve 46, some degree of opening of the valve 46 will require a greater rate of steam flow to produce the same pressure differential required for closing of the switch 48. Conversely, some degree of closing of the valve 46 will require less steam flow through it to effect closing of the switch by the same pressure differential. Accordingly, peak power loads may be set by simply leaving the switch 48 in an adjusted position and adjusting the valve 46 (or the orifice 47 if it is adjustable), for the pressure differential required to actuate the switch.

Another manner of adjusting the kilowatt load at which the switch 48 becomes effective will be hereinafter explained in connection with FIG. 5.

In addition to these adjustable controls by which the operation of the system may be changed for different load limits, the invention also provides means for controlling the electric conductivity of the water by concentration or dilution of its chemical content, so as to compensate for load limit changes, boiler water temperature changes and other such factors which may effect conductivity and, therefore, the rate of generation of steam. It is desirable to control the conductivity so that at zero boiler load, the water level in the boiler is at the minimum 120 below the electrodes, while at maximum boiler load the electrodes are fully immersed in the maximum water level 12a. Maintaining a substantially constant steam pressure at loads between zero and maximum boiler capacity is achieved by the throttling action of the valve 45 as already described, but it will be apparent that if the rated boiler load were to be changed, as for example from 750 kw. to 500 kw. maximum, the maximum water level in the boiler would have to be lowered for the new rating in the absence of a change in conductivity. Since it is best for the electrodes to be fully immersed at the maximum boiler load regardless of the power rating of the boiler, it therefore becomes necessary to change the conductivity of water upon changing of the boiler load.

As already explained, the Water conductivity is controlled by either opening the chemical feed valve 42 so that the conductivity is increased by introduction of more chemical into the water, or by opening the water blowdown valve 44 so that some water is drained from the boiler and replaced by chemically untreated water from the feed conduit 19, thus diluting the concentration and decreasing conductivity.

The chemical feed valve 42 is operated by a solenoid 67 and the water blow-down valve 44 is operated by a. solenoid 68, these two solenoids being in circuit, respectively, with

contacts

69, 70 of the switch 48. The

contacts

69, 70 are actuated concurrently with the aforementioned contact 64 by the switch actuator 66, the contact 69 being in series With a contact 71 of a relay 72, while the contact 70 is in series with a contact 73 of a relay 74. The contact 69 is normally closed and the contact 70 is normally open. The relay 74 is in circuit with the probe 35 at the water level 12b in the level sensing switch 33, While the relay 72 is in circuit with the probe 34 at the maximum Water level 12a.

In operation, if the pressure differential switch 48 indicates that steam generated by the boiler is up to its preset capacity, say 500 kw., the water level in the sensing switch 33 would be at or above the level of the probe 35 corresponding to the boiler water level 12b. If the apparatus is generating steam at full capacity and the water level is below 12b, as sensed by the probe 35, then the water conductivity is too high. In such event, with the switch contact 70 already closed by the steam pressure differential acting on the switch 48, the contact 73 of the relay 74 will become opened and the solenoid 68 will open the water blow-down valve 44 to effect water dilution and lowering of conductivity as already explained.

On the other hand, if the pressure differential switch '48 indicates that steam is being generated at a substantially lesser rate than capacity permits, and the water level is at the maximum 12a as sensed by the probe 34 of the switch 33, then the water conductivity is too low and requires to be increased. Under these conditions the steam pressure differential acting on the switch 48 will not be sufficient to open the switch contact 69 and while the latter remains closed, the contact 71 of the relay 72 will become closed and the solenoid 67 will open the chemical feed valve 42 to effect introduction of more chemical into the boiler for greater conductivity. The increased conductivity will produce a corresponding increase of current flow at the electrodes 11, thus increasing the rate of steam generation at the same water level. The chemical feed valve 42 will remain open until full steam capacity of the boiler is reached at the maximum water level 12a, at which time opening of the pressure differential switch contact 69 will cause the solenoid 67 to close the valve 42.

It will be understood from the foregoing that a definite relationship is thus maintained between the water level in the boiler and the steam pressure drop across the obstruction means 46 or 47 in the steam outlet line 15, which in turn is a measure of steam passing through it. If the water level is too low for a given steam flow or pressure drop, the blow-down valve 44 will open to reduce conductivity of the boiler water. On the other hand, if the water level is too high for a given steam flow or pressure drop, the chemical feed valve 42 will open to increase conductivity. When conductivity is low, sulficient current is not passed at the electrodes to generate steam at the rated capacity even if the electrodes are fully immersed. When conductivity is high, sufiicient current is passed to generate steam at rated capacity even if the electrodes are only partially immersed, which can result in excessive density of current in the boiler water and also in too small a range in boiler water levels between zero and maximum loads to provide adequate control of generated steam pressure. The automatic operation of the

conductivity control valves

42, 44 as a function of water level sensing and steam pressure differential sensing avoids such difficulties.

If the peak power demand of the apparatus is to be changed, say from 500 kw. to 750 kw., the pressure differential switch 48 is adjusted to close the switch contacts 64, 70 and open the contact 69 at a higher differential pressure. In such a change, boiler water having conductivity suitable for operation at a maximum of 500 kw. will not be adequate for operation at 750 kw., and

this discrepancy will be reflected by an unbalance between the newly set steam flow (pressure drop) and the water level in the boiler. For example, water of the same conductivity reacting at the maximum level 12a may use power at the rate of 500 kw., but not at 750 kw. Such a condition will indicate insuflicient water conductivity and will be corrected by opening of the valve 42 to feed more chemical into the boiler. In a similar manner, if the peak power demand is reduced from 750 kw. to 500 kw., there will be excessive water conductivity after the change and the water level at the electrodes will be too low when operating on only 500 kw., although the pressure differential control will limit the load to that much power. Thus, the Water conductivity will be decreased by opening of the blow-down valve 44 for dilution of the boiler water by fresh water coming from the conduit 19.

Reference is now drawn to the modified embodiment of the apparatus shown in FIG. 3 which is much the same as that in FIG. 1 except that the surge chamber 17, instead of being separate from the boiler 10, is embodied in the boiler itself. Thus, the boiler in FIG. 3 consists of an outer shell 75 with upper and lower ends 76, 77 respectively, having the steam outlet line 15 and the water inlet 14 connected thereto, as will be apparent. A tubular partition 78 is secured to and depends from the upper end 76 in spaced relation from the shell 75, the space between the partition and the shell constituting the surge chamber 17. The lower end of the partition 78 is spaced above the lower end 77 of the boiler, so that the interior of the boiler containing the electrodes 11 and the surge chamber 17' are both in communication with the water inlet 14.

The pressure transmitting line 20' extending from the steam outlet line 15 communicates the top of the boiler with the top of the surge chamber 17 as at 79, it being noted that while the interior of the boiler and the surge chamber communicate with each other in the lower or water region, they are separated in the upper or steam region by the partition 78. The arrangement of the sightglass gauges 24, 32 and of the water level sensing switches 25, 33 is much the same as already explained in connection with FIG. 1, so that it need not be repeated in detail. However, it will be observed that the

lines

22, 30, 23, 31 which carry these respective devices are connected at their lower end to a common branch line 80 extending from the boiler shell 75, rather than to the water feed conduit 19. The operation of the apparatus in FIG. 3 is the same as already described in connection with FIG. 1.

Now referring again to the control system for adjusting the conductivity of boiler water under various different maximum power loads, and particularly to the control system afforded by provision of the water level sensing switches 25, 33 in cooperation with the pressure differential switch 48 as described in connection with FIG. 4, this control system is effective with respect to a fixed maximum water level (12a) and a somewhat lower level 12b which is also fixed relative to the maximum level. Such a control system is quite simple and well suited for relatively small steam generators, but in relatively large units where it is important to operate at peak efficiency at all loads, a modified control system shown in FIG. 5 may be utilized. As such, the control system of FIG. 5 employs a differential switch assembly 81 which facilitates operation of the chemical feed valve 42 and water blowdown valve 44 at any Water level in the boiler and a balance between boiler water level and rate of steam generation is maintained throughout the operating range of the unit.

The control system of FIG. 5 is applicable to the apparatus of either FIG. 1 or FIG. 3 by substituting the differential switch assembly 81 for the pressure differential switch 48 and for the water level sensing switch 33. For sake of simplicity of illustration, the switch assem- 8 bly 81 with its connections has been shown by dotted lines in FIGS. 1 and 3, it being understood that if the assembly 81 is used, the

switches

48 and 33 are omitted.

As shown in FIG. 5, the differential switch assembly 81 comprises a steam pressure differential responsive actuator 82 and a water level responsive actuator 83, both of these being of a diaphragm type as shown. One side of the diaphragm of the actuator 82 is connected by a line 84 to the steam outlet line 15 at the high pressure side or upstream from the obstruction means 46, while the other side of the diaphragm of that actuator is connected by a line 85 to the low pressure side or downstream from the obstruction means. The actuator 82 is operatively connected by linkage 86 to a pivotally mounted, toothed sector 87 which meshes with a pinion 88 imparting a partial rotary movement to a cam 89. The cam 89 is shaped to compensate for square root characteristics of steam flow through the obstruction means 46 in representing changes in pressure differential, and movement of the cam is transmitted by a web or strap 90 to a drum 91 mounted for rotation on a suitable shaft 92. A spring 93 reacting between the shaft 92 and the drum 91 Opposes rotation of the drum in the direction in which it is pulled by the web 90, it being understood that the drum is rotatably positioned on the shaft and that the shaft itself is stationary.

The drum 91 is insulated from the shaft 92 and web 90 in any suitable manner and carries a switch arm 94 to which electric current is delivered by a conductor 95. The arm has an angulated end portion provided at its opposite sides with a pair of

contacts

96, 97, both of which are in circuit with the current supply 95. It will be apparent that changes in steam pressure differential across the obstruction means 46 in the steam outlet line 15, as sensed through the connecting

lines

84, 85 of the actuator 82 will cause movement of the linkage 86 in one direction or the other, as indicated by the arrows 98, which in turn will cause movement of the arm 94 in one direction or the other, as indicated by the arrows 99. At one extreme position of the arm 94 (to the left as viewed in FIG. 5), the arm will engage an adjustable, insulated contact 100 which is carried by a suitable support 101 adjacent the arm, the contact 100 being connected by a conductor 102 to the solenoid of the throttling valve 45, so that current flowing from the current supply through the arm 94 in engagement with the contact will cause the throttling valve 45 to close.

The water level responsive actuator 83 has one side of its diaphragm connected by a line 103 to the water feed conduit 19, and the other side connected by a line 104 to the branch 29 of the steam outlet line 15, whereby the actuator 83 reacts to changes in pressure difierential caused by differences in water level in the boiler 10. In other words, as the boiler water level rises, the pressure differential decreases, and vice versa, and the change in pressure differential as sensed through the connecting

lines

103, 104 of the actuator 83 will cause the linkage 105 of the actuator to move in one direction or the other, as indicated at 106. This linkage movement is transmitted by a toothed sector 107, pinion 108, cam 109 and web 110 to a second drum 111, which is mounted on the shaft 92 for rotation independently of the drum 91 and is biased by a spring 112. The drum 111 is also insulated from the shaft 92 and carries an arm 113 having a forked extremity provided with a pair of

contacts

114, 115 which are insulated from each other. The contact 114 opposes the contact 97 on the arm 94 and is connected by a conductor 116 to the solenoid of the chemical feed valve 42. The contact 115 opposes the contact 96 on the arm 94 and is connected by a conductor 117 to the water blow-down valve 44.

It will be understood that not only is the arm 94 movable in one direction or the other as at 99 by the steam pressure differential responsive actuator 82, but the arm 113 is also movable in one direction or the other as at 118 by the water level responsive actuator 83, the movements of the two arms being entirely independent of each other.

Positions of the two arms are so coordinated that when the boiler water level and the steam flow ratios are in proper balance for a particular setting of the obstruction valve 46 representing the peak kilowatt load for the system, the contacts '96, 97 are separated from the

contacts

115, 116 and the arm 94 is also separated from the contact 100. However, if these ratios should become upset because of excessive conductivity of boiler water, and too much steam is being generated for the water level in the boiler needed to produce that amount of steam, the

contacts

96, 115 will close to open the water blow-down valve 44 for dilution of water in the boiler. On the other hand, if not enough steam is being generated for the water level in the boiler, the

contacts

97, 114 will become closed, thus opening the chemicalfeed valve 42 to increase the conductivity of the boiler water.

Both arms 94, 113 have the same arc of travel, say from to 100% and the position of the arm 94 is indicative of the steam flow through the valve 46 between 0% and 100%, for whatever position the valve 46 may be set. Engagement of the arm 94 with the contact 100 will cause the throttling valve 45 to close, thus providing means for controlling the load limit of the boiler.

The control assembly 81 thus maintains a proper balance between steam flow (kilowatt load) and boiler water level (extent of electrode immersion) at all loads and all water levels between 0% and 100%. When the load limit is changed by adjustment of the valve 46, an unbalanced condition will immediately take place, but this will be automatically adjusted, regardless of the load on the boiler.

FIG. 6 shows a chart representing the desired relationship between boiler water level and percent of maximum boiler load. As will be observed, if the boiler load is doubled and a constant relationship between the water level and load is to be maintained, it will be necessary to double the conductivity of the boiler water. Concentration control accomplishes this to provide the desired conductivity regardless of changes in conductivity caused by temperature changes in boiler water, load changes or boiler water concentration.

Some advantages and features of the apparatus of the invention may be summarized as follows:

(1) Use of steam flow to limit electric load in a simple and positive manner;

(2) Assurance of maximum latitude in controlling steam pressure where load limits on the boiler are subject to change;

(3) Positive and rapid adjustment to maintain constant pressure; 4

(4) Maintenance of most eflicient relationship between steam generating load and available electrode surface;

(5) Most effective and eflicient use of electrodes;

(6) Prevention of excessive current densities in boiler water and at electrode surfaces to assure better electrode service and life; and

(7) Positive control of boiler Water conductivity irrespective of variable factors, including boiler water temperature, dissolved solids in boiler Water, electrode erosion, et cetera.

While in the foregoing there have been described and shown the preferred embodiments of the invention, various modifications may become apparent to those skilled in the art to which the invention relates. Accordingly, it is not desired to limit the invention to this disclosure, and various modifications and equivalents may be resorted to, falling within the spirit and scope of the invention as claimed.

What is claimed as new is:

1. In an electric steam generator, the combination of a. boiler containing a vertically elongated electrode immersed in current conductive water having maximum and minimum levels adjacent the respective upper and lower ends of the electrode, a vertically elongated surge chamber having a normal water level substantially at the maximum water level in said boiler, a water feed conduit communicating with the bottom of the boiler and surge chamber, a steam outlet line extending from the top of the boiler, a pressure transmitting line communicating the top of the boiler with the top of the surge chamber, a water feed control valve provided in said feed conduit, means responsive to lowering of the normal water level in said surge chamber for opening said water feed control valve, a throttling valve provided in said pressure transmitting line whereby water may be transferred from said boiler to said surge chamber when the throttling valve reduces pressure in the surge chamber below that in the boiler, first control means responsive to a predetermined steam pressure in said outlet line for actuating said throttling second control means responsive to a pressure diiferential upstream and downstream of obstruction means in said outlet line for actuating the throttling valve independently of said first control means, and a pressure differential valve provided in said steam outlet line for maintaining a constant pressure differential upstream and downstream from said diflerential valve with the downstream pressure being lower than the boiler pressure, and a restricted bleed line communicating said surge chamber with said steam outlet line downstream from said pressure dilferential valve.

2. The apparatus. as defined in claim 1 wherein said surge chamber is constituted by a tank separate from said boiler.

3. The apparatus as defined in claim 1 wherein said boiler includes an outer shell with upper and lower ends, and a tubular partition extending downwardly from the upper end in spaced relation from said shell, said surge chamber being constituted by the space between the shell and the partition.

4. The apparatus as defined in claim 1 together with a Water blowdown valve communicating with said boiler, and water conductivity control means responsive to lowering of water level in the boiler and to steam pressure drop across said obstruction means in said outlet line for opening said blow-down valve when adequate steam is generated at less than appropriate boiler level.

5. The apparatus as defined in claim 1 together with a chemical feeding valve communicating with said boiler, and water conductivity control means responsive to raising of water level in the boiler and to steam pressure drop across said obstruction means in said outlet line for opening said chemical feeding valve when inadequate steam is generated at maximum boiler level.

6. The apparatus as defined in claim 1 together with a water blow-down valve and a chemical feeding valve communicating with said boiler, and water conductivity control means responsive to changes in water level in the boiler and steam pressure drop across said obstruction means in said outlet line for alternately opening said water blow-down valve and opening said chemical feeding valve.

7. In an electric steam generator, the combination of a boiler containing a vertically elongated electrode immersed in current conductive water having maximum and minimum levels adjacent the respective upper and lower ends of the electrode, a vertically elongated surge chamber having a normal water level substantially at the maximum water level in the boiler, a water feed conduit communicating with the bottom of the boiler and surge chamber, a steam outlet line extending from the top of the boiler, a pressure transmitting line communicating the top of the boiler with the top of the surge chamber, a water feed control valve provided in said feed conduit, means responsive to lowering of the normal water level in said surge chamber for opening said water feed control valve, a throttling valve provided in said pressure transmitting line whereby water may be transferred from 11 said boiler to said surge chamber when the throttling valve reduces pressure in said surge chamber below that in the boiler, obstruction means provided in said steam outlet line, means for sensing pressure differential upstream and downstream of said obstruction means, said pressure differential sensing means being operative to throttle said throttling valve when a predetermined difference in pressure is reached, a water blow-down valve and a chemical feeding valve communicating with said boiler, means for sensing changes in water level in the boiler, water conductivity control means responsive to said pressure differential sensing means and to said water level sensing means for opening said water blow-down valve and closing said chemical feeding valve when a predetermined pressure differential is reached at less than maximum water level and, conversely, for closing the water blow-down valve and opening the chemical feeding valve when a predetermined pressure differential is not reached at maximum water level in the boiler, and a restricted bleed line communicating said surge chamber with said steam outlet line downstream from said obstruction means.

8. The apparatus as defined in claim 7 wherein said water level sensing means are fixed with respect to the maximum water level in said boiler for cooperation with said pressure differential sensing means.

9. The apparatus as defined in claim 7 wherein said water level sensing means are variable with respect to the maximum water level in said boiler for cooperation with said pressure differential sensing means.

10. The apparatus as defined in claim 7 together with means responsive to a predetermined steam pressure differential in said outlet line at a point downstream from said obstruction means for throttling said throttling valve independently of'said pressure differential sensing means.

11. The apparatus as defined in claim 7 wherein said surge chamber is constituted by a tank separate from said boiler.

12. The apparatus as defined in claim 7 wherein said boiler includes an outer shell with upper and lower ends, and a tubular partition extending downwardly from the upper end in spaced relation from said shell, said surge chamber being constituted by the space between said shell and the partition.

References Cited UNITED STATES PATENTS 2,546,889 3/1951 Eaton 219284 X 2,598,490 5/1952 Berg et al. 219287 2,961,525 11/1960 Riker 219-284 X FOREIGN PATENTS 523,419 4/1956 Canada. 531,966 10/1956 Canada.

JOSEPH V. TRUHE, Primary Examiner MARTIN C. FLIESLER, Assistant Examiner U.S. Cl. X.R. 219286, 287