US2450061A - Electric boiler - Google Patents

Description

Sept. 28, 1948. A. A. SMITH ELECTRIC BOILER File d Sept. 24, 1945 M Arno/d Aim/W2 Momma Patented Sept. 28, 1948 ELECTRIC BOILER Arnold A. Smith, Three Rivers, Quebec, Canada, assignor to International Paper Company, New York, N. Y., a corporation of New York Application September 24, 1945, Serial No. 618,101

v It is an object of this invention to provide a control system for electric boilers of the conductiontype, which is highly adjustable without being subject to hunting. 1 i

It is a further object of this invention to provide a system of control which operates regardless of changes in electrode condition or scale formation, and at all times within safe limits of water level and current densities.

.It, is a further object of this invention to provide'acontrol system wherein water density is held at,-or near, the maximum permissible, resulting in minimum blow-down with consequent minimum losses.

The above and other objects will be made clear from the following detailed description taken in connection with the annexed drawing which represents, schematically, a particular application of the improved boiler control system.

"The fundamental principle of an electric conduction boiler is extraordinarily simple. A boiler drum is provided in which is mounted an electrode. The electrode is partially submerged and is surrounded by a metal shell, also partially sub-- merged; The shell is grounded and current flows from the electrode to the shell, thence to the ground, passing through the water, which is in contact with both the electrode and the shell. The .water offers substantial resistance to the passage of the current, and the current encountering this resistance, generates suiiicient heat to boil the water. For all practical purposes, the voltage applied is a constant. The amount of current drawn by the system varies, therefore, inversely with the resistance; and since the heatingeffect is the product of resistance, times the square of the current, the total power input varies inversely as the resistance. The resistance of boiler water depends on the temperature and pressure, and more particularly upon the quantity and nature of the solids in solution in the water. Over any reasonable period of time, however, these factors may be considered constant; and with these factors constant, resistance is inversely proportional to the depth of immersion of the electrode. Since power input varies inversely with resistance, and resistance in turn varies inversely with depth of immersion, power input is a direct function of the depth of immersion.

Given any form of control over the rate of addition of feed water to a boiler chamber as above described, it is possible to meet fluctuations in demandfor steam from the boiler by adjusting the depth of immersion of the electrode. It is not, however, sufficient merely to be able to make 4 Claims. (01. 219-40)- 2 an adjustment. approximately 8 cubic feet of steam are required per minute in order to supply a demand of 1 boiler horsepower. If such a demand were not met for a period of one minute, the pressure would drop topounds. tial that the response of the control system .to a change in the demand be as prompt, and as positive, as possible. The present invention assures promptness of response by constantly conditioning the water to be supplied to a boiler chamber, so that water enteringthe chamber will always be at a temperature closely approximating (within 10%) the temperature of the water already inthe boiler." r This system isdescribed hereinafter,

with referenceto a three phase, three body, installation, as being the type of installation ordinarily most difficult to control. The principles are, however, equally applicable to a three phase, single bodyinstallation, or to any other combination.

in the drawings, there are shown threeboiler chambers l 0, 2B and 30, in each of which is mounted an electrode, respectively designated 12, 22'

and 32. Surrounding each electrode is an electrically grounded shell, respectively designated I4, 24, and 34. A surge tank 50 is provided, which has-a pressure equalizing connection 52 with each of the boiler chambers 10, 20 and 30, through parallel steam lines,- respectively designated i6, 26 and 36. The lines It, 26 and 36 are steam delivery lines feeding a joint delivery line 84. At the bottom of the surge tank 50 is a conventional blow-down valve 52 and a water outlet 54 conmeeting with a pump 56. The ump 56 delivers toa water line 58 which is connected with the boiler chambers l0,'20 and 30, by means of parallelconnections, respectively designated I8, 28 and 38. Water constantly leaves the boiler chambers Ill, 20 and 30 through connections, respectively designated I I, 2| and 3!, and, impelled by pumps I 3, 23 and 33, is delivered to a line 30 by means of parallel connections !5, 25 and 35. The line '60 delivers water to the surge tank 50. The activity of pumps 13, 23 and 33 and of the pump 56, is such, normally, as to provide a rate of cir-. culation of water through the boiler chambers I0, 20 and 30 equal to approximately five times the normal rate of steam delivery (in weight per unit oftime) from each of the boiler chambers.

Make up feed water is delivered to the surge tank 50 through a line 62. The rate of delivery is controlled'by a valve 64, which is automatically At pounds gauge pressure,

It is, therefore, absolutely'essen connected therewith an automatic level control, designated respectively as l1, 2? and 31. A main control 80 is connected by a sensing line 82 to the discharge line 84, which receives steam delivered from the three boiler chambers Ill, 20 and 30. Control impulses from the regulator 80 are delivered to the level controls ll, 21 and 31 through control lines l1, '2'! and 31, respectively. The level control I! is connected by a line H! to a valve IS in the line l5, and by a line IT" to a valve IS" in the line l8. The control 21 is connected by a line 29 to a valve 29' in the line 25, and by a line 21" to a valve 29 in the line 28. The level control 31 is connected by a line 39 to a valve 39 in the line 35, and by a line 31" to a valve 39 in the line 38.

The level of water in the boiler-chamber l may be adjusted upward by opening the valve I9" and closing the valve I9, and may be lowered by the reverse adjustment of these valves. So long as pressure in the line 84 remains substantially constant, the level control l1 operates the valves 19' and [9" to maintain substantially a constant level of water within boiler chamber 10. :The level control 21 operates in precisely the same way on valves 29" and 29 to control the water level in the boiler chamber 20, while the control 31 and the valves 39 and 39 operate in thersame manner as to boiler chamber 30.

.When the steam demand increases, there will bea drop in the pressure in the delivery line 84, which. drop will affect-the controller 80. The controller 80, through lines I1, 2'! and 3'1, will override the normal control of the controllers I1,

21 and 37, causing these to close valves I9, 29

and 39, .while opening valves I9, 29 and 39". The circulation system, at this point, operates to fill the boiler chambers 10, and 3!], drawing upon water in the surge tank 50. When a level is reached in the boiler chambers I0, 20 and .30, which results in increasing the steam delivery rate to a point at which the desired pressure is attainedin the line 84, the effect of the controller 80 is eliminated and the units ll, 21 and 31 resume control, maintaining the level in drums Ill, 20 and at the new point.

When there is a sudden drop in the steam demand, there will be a rise in pressure in the line 84. This pressure increase afiects the overriding control 80, which in turn operates the units I1, 21 and 31 causing these to open. the valves I9, 29 and 39, and to close the valves I9, 29', and 39". This setting withdraws water from the boiler chambers I0, 20 and 38, and delivers the water to the surge tank 50.

The water delivery valve 64 in the feed water line 62 is under the control of a unit B6 through a line 68. The control 66 responds to the levelin the surge tank 50. The normal operation of the surge tank calls for the level in said tankto be low'during a period of high demand on the line 84, and to be high durin a period of low demand. At all times, pressure in surge tank 50 is the same as the pressure in line 84 and in the boiler chambers I3, 20 and 30, and there isa constant cir- These losses occur on thesteam side, to

bring about a current density sufiiciently great to cause dissociation with constant gassing. To guard against this condition, a bleeder valve III i inserted in the circulation line 60. The valve 70 is operated by a conductivity controller 12 through a line 14. When the specific conductivity of the water attains a predetermined value, the controller 12 opens the valve 10 and bleeds water out of the system until the addition of feed water through the line 62 brings about sufficient dilution to lower the specific conductivity. The operation of the controller 12 and the valve 10, due to the high rate of circulation, is sufficiently prompt to avoid excessive bleeding, and the avoidance of r such excess produces great economies over any substantial period of time.

All of thecontrollers mentioned herein are of standard types and may be bought from a numberof sources, such, for example, as the Bailey Meter Company, Foxboro Company, and The Mason'Regulator Company. For this reason, the mechanical details of the several controllers have been omitted and the system has, generally been illustrated schematically.

The provision of the surge tank 50 brings about number of advantages. .With the high rate of circulation .(five times average demand) and the controlled addition of feedwater, incomin feed Water has less than a 10 percent effect on the temperature of water going to the boiler chambers. In addition, the mineral content of the incoming feed water, so far as such content will precipitate under heat, precipitates in the surge tank 5%) and collects at the bottom where it may be removed by an ordinary blow-down, using valve-.52. The pumping system which handles water ata rate approximating five times the ormal steam demand, is not, as it might seem, an extravagant consumer of power, since most of the time the pumps operate against only a relatively low gravity head and, never operate. against full steam pressure. however, makes it possible to bring about a rapid adjustment of level in the boiler chambers and thus to provide extremely prompt response. to a change in steam demand. During any period of steady steam demand, the controllers ll, Hand 31 operate to maintain the requisite level, whether high .or low, suitable to meeting such. demand. The controller, operates only when the. static pressure in line 84 exceeds or drops below a predetermined point. There is provided, therefore, individual control of the several boiler chambers, operative during any prolongedlevel 'of demand, such individua1 control, however, being overridden by the universal control 80 whenever abnormal fluctuations of demand occur.

I claim:

1. In a boiler, a boiler chamber, at least one electrode positioned therein and adapted to be partially submerged in water, an electrically grounded baffle surrounding and spaced from said electrode, a separate surge tank, a pressure'equalizingconnection between said boiler chamber and said surge tank, a first pump for positively pumping water from said boiler into said surge tank, asecond pump for positively pumping water'irom said surge tank into said boiler, said first. and second pumps being capable of handling water at a rate in weight per unit of time'greater. than the maximum rate of steam delivery. from said boiler chamber, and means responsive to steam demand for controlling the relative outputs of said first and second pumps to raise or lower the depth of submersion of saidelectrode.

This high rate of circulation,

2. In a boiler, a boiler chamber, at least one electrode positioned thereinand adapted to be partially submerged in water, an electrically grounded baille surrounding and spaced from said electrode, a separate surge tank, a pressure equalizing connection between said boiler chamber and said surge tank, a first pump for positively pumping water from said boiler into said surge tank, a second pump for positively pumping water from said surge tank into said boiler, said first and second pumps being capable of handling water at a rate in weight per unit of time greater than the'maximum rate of steam delivery from said boiler chamber, means responsive to steam demand for controlling the relative outputs of said first and second pumps to raise or lower the depth of submersion of said electrode, and means responsive to a range of water level variations within said surge tank for controlling the supplyin of make-up feed water thereto.

3. In a boiler, a boiler chamber, at least one electrode positioned therein and adapted to be partially submerged in water, an electrically grounded baille surrounded and spaced from said electrode,a separate surge tank, a pressure equalizing connection between said boiler chamber and said surge tank, a first pump for positively pumping wateri'rom said boiler into said surge tank, a second pump for positively pumping water from said surge tank into said boiler, said first and second pumps being capable of handling water at a rate in weight per unit of time greater than the maximum rate of steam delivery from said boiler chamber, means responsive to steam demand for controlling the relative outputs of said first and second pumps to raise or lower the depth of submersion of said electrode,means responsive to a range of water level variations within said surge tank for controlling the supplying of makeup feed water thereto, and means responsive to the specific conductivity of the water leaving said chamber for bleeding water from the system to restore dilution to a predetermined value.

4. In a boiler system, a plurality of boiler chambers having a common delivery line, an electrode in each of said chambers adapted to be partially submerged in water, an electrically grounded baflle surrounding and spaced from said electrode, a single surge tank separated from said boiler chamber, a, series of parallel connected pressure equalizing connections between said surge tank and each of said boiler chambers, a pump associated with each of said boiler chambers for withdrawing water therefrom and pumping the same into said surge tank, a series of parallel connected pipes connecting said pumps with said surge tank, a pump associated with, said surge tank for pumping water rtherefrom into each of said boiler chambers, a series of parallel connected pipes connecting said pump with each of said boiler chambers, the said pumps together maintaining water circulation at a rate in weight per unit of time greater than the rate of steam delivery from said boiler chambers, means responsive to steam demand for controlling the relative flow of water through the several branches of all of said parallel connected, pipes to individually raise or lower in each of said boiler chambers the depth of submersion of said electrodes, and means responsive to a range of water level in variations within said surge tank for effecting the supplying of make-up feed water thereto.

ARNOLD A. SMITH.

REFERENCES CITED The following references are of record in the file" of this-patent:

UNITED STATES PATENTS Number

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