CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of the filing date of U.S. Provisional Application No. 63/311,160, filed on February 17, 2022, entitled “Steam Generator,” the disclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] One aspect of the present invention relates to electrode boilers. As used in this disclosure, the term “boiler” refers to a structure which is adapted to boil a liquid in normal operation of the structure so as to generate a vapor. An “electrode boiler” is a structure having electrodes connected to an electrical power supply and disposed in a structure holding an electrically conductive liquid, so that the liquid can be heated and boiled by directing an electric current between the electrodes through the liquid. Electrode boilers are most commonly used to generate steam for industrial processes. Examples of electrode boilers are shown in GB2196820; GB2072898; DE402950; and CN111322600 (A).

[0003] The electrode arrangements used in electrode boilers differ from those used in devices which are intended for use in heating a liquid without boiling. Examples of those devices are shown in US 2010/0322605; US7817906; WO2020231386 and WO2018085773. As described for example in WO2018085773, such devices may include numerous electrodes disposed in contact with the liquid, the electrodes being arranged so that different sets of electrodes define conductive paths through the liquid having different specific resistance. As used in this disclosure, the term “specific resistance” is used with reference to a circuit or a part of a circuit having elements electrically connected by a fluid. The specific resistance is the ratio between the electrical resistance of the circuit or part of a circuit and the resistivity of the fluid in the circuit. The control system actuates switches to connect different sets of electrodes to the power supply so as to control the power dissipation in the liquid and maintain a desired liquid output temperature despite variations in conductivity of the liquid, the liquid flow rate and liquid input temperature. Such a system depends on the spaces between the electrodes being entirely filled with the liquid, and has not been applied to boilers heretofore. BRIEF SUMMARY OF THE INVENTION

[0004] One aspect of the invention provides a boiler. A boiler in accordance with this aspect of the invention desirably includes a structure having vertically-extensive walls defining multiple vertically-extensive channels. The structure desirably includes a liquid supply connection communicating with liquid inlets adjacent a lower end of each of the channels and a vapor discharge communicating with liquid outlets adjacent the upper end of each of the channels. The boiler desirably also includes a set of electrodes positioned within the channels, with some of the electrodes in each channel being located at different elevations. An electrical power supply of the boiler desirably has at least two poles and is operable to supply different electrical potentials to the different poles. The boiler desirably also has a circuit operable to selectively connect the electrodes to and selectively disconnect electrodes from the poles in multiple different connection schemes, each of which involves electrical current flowing between the connected electrodes along a current path through liquid in at least one of the channels.

[0005] The circuit of the boiler in accordance with the above aspect of the invention may be operative to selectively connect isolated electrodes which are not connected to the poles of the power supply and which are disposed in different channels to one another. In at least one of the connection schemes, the current path may extend through liquid in a plurality of channels and through the isolated electrodes.

[0006] In accordance with some of the above aspects of the invention, the structure may define an upper space communicating with the outlets of the channels and extending above the outlets of the channels, and the vapor discharge may communicate with the outlets of the channels via the upper space. The boiler in accordance with some aspects of the invention may further include a liquid level control system that is operative to maintain a liquid level in the upper space about the outlets of the channels. In accordance with at least some aspects of the invention, the boiler may further include a set of baffles located in the upper space. Such baffles may be arranged to define a tortuous path for vaper rising within the upper space. Such baffles may alternatively, or additionally, be arranged to allow entrained liquid which drops out of the vapor to drain downwardly. [0007] In accordance with some of the above aspects of the invention, the set of electrodes disposed in each channel may include a plurality of pairs of electrodes, where the electrodes of each pair confront one another.

[0008] In accordance with some of the above aspects of the invention, the boiler may further include a control system that is operative to repeatedly select a connection scheme from the plurality of connection schemes and command the circuit to connect the electrodes in the selected connection scheme. Such control system may be operative to detect the presence of vapor in current paths associated with various connection schemes and to substantially prevent prolonged operation with those connection schemes having vapor present. The control system may further be operative to select a connection scheme, connect the electrodes in the selected connection scheme, monitor the actual current passing between the poles of the power supply, compare the actual current to an expected current for the selected connection scheme, and select a new connection scheme if the actual current is less than the expected current by more than a current tolerance.

[0009] In accordance with some of the above aspects of the invention, the structure of the boiler may include a vessel and a plurality of dielectric walls disposed within the vessel and defining the channels. Such dielectric walls may be plates extending substantially parallel to one another.

[0010] Another aspect of the invention provides a device for heating a conductive liquid. A device in accordance with this aspect of the invention desirably includes a structure defining multiple channels extending side-by-side and having dielectric walls between each of the channels, where means are included for directing the liquid through the channels. The boiler desirably also includes a set of electrodes within each channel that include electrodes positioned at multiple locations along the length of the respective channel. An electrical power supply of the device desirably has at least two poles and is operable to supply different electrical potentials to the different poles. The device desirably also has a circuit operable to selectively connect the electrodes to and selectively disconnect electrodes from the poles in multiple different connection schemes, each of which involves electrical current flowing between the connected electrodes along a current path through liquid in at least one of the channels. The circuit is desirably operable to select isolated electrodes of two different sets which are not connected to a pole of the power supply and connect the selected isolated electrodes to one another so that the current path extends between the connected electrodes through the isolated electrodes.

[0011] Another aspect of the invention provides a boiler. A boiler in accordance with this aspect of the invention desirably includes a vessel having a liquid inlet and a vapor outlet. The boiler desirably also includes multiple electrodes positioned within the vessel and located in an array extending vertically and in at least one horizontal direction, such that some of the electrodes are disposed at a higher level than others and some of the electrodes are horizontally offset from others. An electrical power supply of the boiler desirably has at least two poles and is operable to supply different electrical potentials to the different poles. The boiler desirably also has a circuit operable to selectively connect the electrodes to and selectively disconnect electrodes from the poles in multiple different connection schemes, each of which involves electrical current flowing between the connected electrodes along a current path through liquid in the vessel. The boiler in accordance with this aspect of the invention desirably also has a control system operative to repeatedly select a connection scheme and command the circuit to connect the electrodes in the selected connection scheme. The control system is desirably operative to detect the presence of vapor in current paths associated with various connection schemes and to substantially prevent prolonged operation with those connection schemes having vapor present.

[0012] Another aspect of the invention provides a method of operating a heater. The method in accordance with this aspect of the invention desirably includes the steps of:

(a) contacting a plurality of electrodes with an electrically conductive liquid;

(b) selectively connecting electrodes of the plurality of electrodes to establish a conduction path between poles of a power supply through the liquid;

(c) applying a voltage between the poles to heat the liquid and measuring an actual current flowing through the conduction path;

(d) comparing the actual current to an expected current for the conductive path; and

(e) repeating steps (b) through (e) with a different selection of electrodes to establish a different conduction path when the comparison performed in step (d) indicates that the actual current is less than the expected current by more than a current tolerance. [0013] In accordance with some of the above aspects of the invention, step (b) may include setting a desired heating rate in response to measurements of one or more parameters indicating a result achieved by heating the liquid, as well as selecting the electrodes and the current path based on the desired heating rate. In accordance with at least some of the above aspects of the invention, the liquid may boil during steps (a)-(e).

BRIEF DESCRIPTION OF THE DRAWING

[0014] The FIGURE is a schematic, vertical section view of an electrode boiler for generating steam according to an embodiment of the invention.

DETAILED DESCRIPTION

[0015] A boiler according to one embodiment of the invention includes a vessel 10 having vertically extensive side walls 12 and 13 on opposite sides, a bottom wall 14 and a top wall 16. The vessel also has front and rear walls (not shown), so that the vessel is closed apart from an intake opening 44 in the bottom wall and a discharge opening 38 in the top wall. As used in this disclosure, terms such as “top”, “bottom”, “vertical”, “above” and “below” are used with reference to the boiler as installed in an operative position in the normal gravitational frame of reference. The term “vertically extensive” means that the element discussed extends in the vertical direction, but does not require a perfectly vertical orientation; the element discussed may also extend in the horizontal direction.

[0016] Vertically extensive interior walls 20, 22 and 24 are disposed within the vessel. The interior walls extend into and out of the plane of the drawing in the FIGURE, and desirably from the front wall to the back wall. The interior walls together with side walls 12 and 13 thus divide the space with the vessel into four channels 26, 28, 30, and 32. The interior walls terminate above bottom wall 14 and below top wall 16, so that there is a lower space 34 below the channels and an upper space 36 above the channels. Each channel has an inlet adjacent the lower end of the channel open to lower space 34 and an outlet adjacent the upper end of the channel open to upper space 36.

[0017] A set of electrodes is disposed within each of channels 26, 28, 30, and 32. The set of electrodes disposed within each channel includes pairs of opposed electrodes spaced apart from one another. In this embodiment, the opposed electrodes are mounted on opposite walls of the channel. The pairs of electrodes within each channel are spaced apart from one another along the length of the channel so that they are disposed at different vertical levels. For example, the electrode set disposed in channel 32 includes, in ascending level order, pair of opposed electrodes 32-1 A and 32- IB; pair of electrodes 32-2A and 32-2B; pair 32-3 A and 32-3B and pair 32-4A and 32-4B. All of the electrodes designated with letter “A” are mounted to wall 24, whereas the electrodes designated with letter B are mounted to vessel side wall 12. In this embodiment, the electrodes of the middle pairs 32-3 A and 32-3B; and of 32-2A and 32-2B are of the same size. The electrodes of the lowest pairs 32-1 A and 32- IB; and the upper pairs 32-4A and 32-4B are of the same size but smaller than of the middle pairs. The electrodes disposed in the other channels are identical to the electrodes in channel 32, and are disposed in the same arrangement. Thus, the electrodes mounted to each of the interior walls 20, 22, and 24 are disposed in back-to-back alignment with one another. For example, electrode 30-4B disposed in channel 30 is in back-to-back alignment with electrode 32-4A in channel 32.

[0018] The vessel side walls 12 and 13 and interior walls 20, 22, and 24 are each dielectric walls. These walls may be formed entirely from dielectric materials or may have a layer of a dielectric material at the surface or surfaces which carry the electrodes. In either case, the dielectric wall cannot conduct electrical current from one channel to another.

[0019] The vessel has a vapor outlet opening 38 disposed at or near the top of the vessel. A set of baffles 40 are disposed in the top space 36 below vapor outlet opening 38. The baffles are arranged to define a tortuous path for vapor rising within the upper space, and to allow entrained liquid which drops out of the vapor to drain downwardly. A vapor delivery conduit 42 is connected to outlet opening 38 to deliver vapor to a point of use.

[0020] The vessel has a liquid inlet 44 communicating with the lower space 34. A liquid source 46 is connected to the liquid inlet. Source 46 is controllable so as to vary the flow of liquid into the vessel. This variation may be stepwise such as either off, with no flow, or on with a predetermined flow, or may be progressive from no flow to a maximum flow rate. For example, source 46 may include a connection to a utility liquid supply and a valve, or a variable-rate pump connected to a tank of liquid. [0021] The boiler further includes an electrical power supply 50 having opposite poles 51 and 53. The power supply is arranged to apply different electrical potentials to the two poles. For example, one pole may be a “neutral” pole having a fixed potential, and an alternating potential may be applied to the other pole.

[0022] A switching circuit 52 is connected to the poles of the power supply and to a control system 54. The switching circuit typically includes numerous semiconductor switches (not shown) such as MOSFETS, JFETS and the like, although other forms of switches such as relays responsive to control signals may be used. The switching circuit is arranged to selectively connect certain electrodes to the poles of the power supply and to connect other electrodes to one another according to connection schemes selected by the control system. These connection schemes define conduction paths between the poles of the power supply through the conductive liquid in the boiler. For example, in a first connection scheme where electrodes 26-2A and 26-2B are connected to the poles and all of the other electrodes are disconnected from the poles, the conduction path extends only within the space between these electrodes, as schematically shown by line 60. In a second connection scheme, electrodes 26-3A and 32-3B are connected to the poles of the power supply whereas each of the following pairs of back-to- back electrodes are disconnected from the poles but connected to one another: 26-3B and 28-3A; 28-3B and 3O-3A; and 3O-3B and 32-3A. This connection scheme forms a conduction path 62 though the liquid in all four channels, which is longer than conduction path 60. For a given voltage applied by the power supply and a given conductivity of the liquid, conduction path 62 will have a lower current flow and lower power dissipation than conduction path 60. Stated another way, the second conduction scheme with path 62 has a higher specific resistance than the first connection scheme with path 60. The second connection scheme with conduction path 62 is an example of a “straight across” conduction path in that it extends only between electrodes disposed at the same elevation, i.e., electrodes at the third level. In a third connection scheme, electrodes 26-1 A and 32- IB are connected to the poles, and each of the following of the following pairs of back-to-back electrodes are disconnected from the poles but connected to one another: 26-4B and 28-4A; 28- IB and 30-1 A; and 30-4B and 32-4A. In this connection scheme, the conduction path 64 zigzags between electrodes at levels 1 and 4, and thus extends lengthwise within each channel so as to provide a much longer current path through the liquid. The third connection scheme thus provides an even higher specific resistance and lower current than the second connection scheme. In still other connection schemes, multiple current paths can be provided between the poles, so that these connection paths are electrically connected in parallel to provide a lower specific resistance. Electrodes which are not directly connected to the poles are referred to herein as “isolated electrodes”. For example, the pairs of back to back connected electrodes included in the connection schemes discussed above are isolated electrodes. Of course, the connection schemes discussed above are merely exemplary; the electrodes and switches can provide numerous different connection schemes with numerous and widely varying specific resistances. It is not essential to provide the capability for every electrode to be connected in every possible way. For example, the switching circuit may be incapable of connecting some back-to-back electrodes to one another. This would reduce the number of available connection schemes, but would also reduce the cost of the switching circuit. Conversely, to provide even more versatility, the switching circuit may be arranged to connect isolated electrodes which are not back-to-back with one another. For example, the switching circuit may allow for connection of electrodes 28-3B and 32-3A with one another through a shunting bus (not shown). This would modify conduction path 62 so that the current passing along the path bypasses the liquid in channel 30, and thus provide a lower specific resistance.

[0023] The boiler includes a level sensor 72 operative to measure a liquid level in upper space 36. The level sensor may be a float sensor, ultrasonic sensor or other conventional device. The level sensor is operatively linked to liquid source 46 so that the liquid source acts to maintain a liquid level slightly above the interior walls 20, 22, and 24 and thus slightly above outlets of channels 28-32. The operative connection between the level sensor and the liquid source may be through control system 54 or through a separate feedback circuit or linkage.

[0024] A temperature sensor 70 is adapted to measure the temperature of liquid in a space between a pair of opposed electrodes 26-1 A and 26- IB near the inlet of channel 26. The boiler also includes one or more sensors adapted to measure a condition indicative of the vapor output from the boiler. These sensors may include a flow rate sensor 74 connected to the output opening 38; a pressure sensor 76 operative to measure pressure in the upper space, and an outlet temperature sensor 78 arranged to measure the temperature of vapor within the upper space. An inlet flow sensor (not shown) measuring liquid inflow through inlet 44 also may be provided. A current sensor 80 is operative to measure the electrical current passing between the poles of the power supply 50. All of the sensors are operatively connected to the control system 54.

[0025] Control system 54 includes a logic circuit 56 and a memory 58. For example, logic circuit 54 may be a programmable element such as a microprocessor. Memory 58 stores the data discussed below and desirably also stores instructions which direct the logic circuit to perform the functions discussed below. The control circuit also includes conventional interfacing circuitry (not shown) to receive signals from the various sensors and conventional drive circuitry (not shown) to convert outputs from the logic circuit to control voltages applied to the switches. Although the control system 54 is depicted as a single unit in the FIGURE, the elements of the control system may be physically separated from one another. Likewise, memory 56 may include plural physical elements, and logic circuit 54 also can include plural physical elements.

[0026] Memory 54 stores a list of the possible connection schemes. The entry in the list for each connection scheme includes the required settings for the switches to enable the connection scheme. The entry for each connection scheme also includes a current parameter representing the expected current flow between the poles when the connection scheme is operated and all of the spaces between the electrodes included in the connection scheme are liquid. For example, the current parameter may be the specific resistance between the poles of the power supply when the electrodes are connected according to the connection scheme. For a power supply having a given voltage between the poles and for liquid having a given conductivity, the expected power dissipation and the expected current are inversely proportional to the specific resistance. The current parameter can also be the current which flows between the poles when the electrodes are connected according to the scheme with liquid of a known conductivity. The entry for each connection scheme also includes elevation data representing the elevation of part or all of the conduction path established by the conduction scheme. In this embodiment, the elevation data is elevation parameter representing the elevation of the highest space between opposed electrodes included in the conductive path established by the connection scheme. For example, all of the electrodes in conduction path 62 are disposed at level 3, and the conduction path thus passes only through spaces between electrodes at level 3. Accordingly, the elevation parameter for the connection scheme associated with conduction path 62 denotes level 3. Conduction path 64 passes through electrodes 26-4B and 28-4A disposed at level 4, and the elevation parameter for the association connection scheme denotes level 4.

[0027] The control system desirably includes means for monitoring the conductivity of the liquid passing into the boiler. In this embodiment, the system is arranged to monitor the conductivity of the liquid at the inlets to the channels by momentarily switching to a connection scheme which establishes a conduction path extending between electrodes 26-1 A and 26- IB and monitoring the current passing along this conduction path. In a variant the boiler may include a separate pair of monitoring electrodes (not shown) disposed adjacent the intake opening 44, and the temperature sensor 70 may be disposed between these electrodes. The control system may intermittently actuate the switches to disconnect the other electrode from the power supply, connect the monitoring electrodes to opposite poles of the power supply and measure the current passing between the poles. In either arrangement, the conductivity of the liquid can be calculated from the current measured by sensor 80 and the known specific resistance of the selected conduction path. In either arrangement, the conduction path used for conductivity determination is at a location near the bottom of the boiler, where boiling is does not occur during normal operation. It is not necessary to calculate the conductivity explicitly; the current measured between the monitoring electrodes can be used directly in determining the expected current for any connection scheme. The conductivity measurement desirably is performed at startup and intermittently after startup.

[0028] In operation, the level sensor 72 and liquid source 46 cooperate to maintain the liquid level in the vessel above the outlets of the channels. The control system selects a connection scheme and actuates the switches to connect the electrodes according to the selected connection scheme. At startup, when pressure sensor 76 and temperature sensor 78 indicate that the boiler is not producing any vapor, the control system may select a connection scheme with an expected current at or near the maximum allowable current and which has a high elevation parameter.

[0029] The control system monitors the current passing between the poles and the vapor output from the boiler. The control system calculates the expected current for the selected connection scheme under based on the current parameter for that connection scheme and the conductivity of the liquid in the boiler as determined by the conductivity measurement discussed above. Optionally, the control system may apply a correction factor to the conductivity of the liquid. The correction factor is based on an estimated temperature of the liquid in each space included in the conduction path and the known relationship between conductivity of liquid and temperature. For example, when the upper space 36 is filled with vapor, the temperature in each space disposed at level 4, near the tops of the channels, can be taken as the boiling temperature of liquid at the pressure indicated by pressure sensor 76, whereas the temperature in each space at level 1 may be taken as the temperature indicated by temperature sensor 70. The temperatures in spaces at levels 2 and 3 can be estimated by interpolation between these values. If the actual value of the current is below the expected current by more than a current tolerance, this indicates that one or more of the spaces between the electrodes included in the connection scheme is at least partially filled with vapor.

[0030] In this condition, the control system attempts to select a new connection scheme having the same expected current but having a lower elevation parameter. If such a connection scheme is found, the control system selects that connection scheme. If not, the control system selects a new connection scheme having a higher expected current and a lower elevation level if the vapor output is below the output setpoint and if the higher expected current will not exceed the maximum allowable current. If the next available higher expected current would exceed the maximum available current, or if the vapor output is below the output setpoint, the control system selects a new connection scheme having lower expected current and lower elevation parameter.

[0031] Regardless of the current monitoring process and vapor detection process discussed above, if the vapor output from the boiler is above the output setpoint by more than an output tolerance, the control system selects a new connection scheme with a lower expected current. If the vapor output is below the output setpoint by more than the output tolerance, the control system selects a new connection scheme with a higher expected current. When the control system selects a new control scheme in response to deviation from the vapor setpoint, if several connection schemes have the desired higher or lower expected current, the control system initially selects the one having the highest elevation parameter.

[0032] Using the control scheme discussed above, the system avoids prolonged operation with any connection scheme which passes through a space with substantial vapor present; if it selects such a connection scheme, it will detect the presence of vapor and shift immediately to another connection scheme.

[0033] With the control scheme discussed above, boiling typically begins at or near the tops of the channels, with vapor bubbling up through the liquid above the outlets of the channels. The vapor rises through upper space 36 and passes out of the vessel via vapor delivery line 42. Although some minor amounts of liquid may be entrained by the vapor, this liquid will impinge on baffles 40 and drain back downwardly into the vessel. As boiling continues, the spaces between electrodes at higher elevations become filled with a mixture of vapor and liquid. The control system responds by shifting the current paths to lower elevations. Under steady-state conditions, the system tends to settle in a condition where boiling occurs near the midpoints of the channels, and the vapor rises to the outlets and through the overlying liquid. Stated another way, the control scheme avoids forming large bubbles of vapor at or near the bottom of channels filled with liquids. This substantially prevents ejection of columns of liquid upwardly into the upper space, which might overwhelm baffles 40 and send a bolus of liquid into the vapor delivery line 42.

[0034] In operation of a boiler, minerals and other constituents dissolved in the liquid supplied to the boiler are left in the boiler. This buildup typically causes the conductivity of the liquid in the boiler to increase. The boiler can be flushed with fresh liquid to remove the buildup of constituents. This may be done periodically or in response to an increase in conductivity detected by the control system. For example, the control system can deactivate power supply 50 and level sensor 72, and then activate the liquid supply to direct fresh liquid through the boiler and out through discharge opening 38. During this operation, a diverter valve (not shown) directs the liquid passing through the discharge opening away from vapor delivery conduit 42 and into a drain (not shown). After the liquid flush, the liquid level can be restored by stopping or restricting liquid flow into the boiler and activating electrodes to boil liquid in the vessel until the sensor 72 indicates the liquid in the vessel is at the desired level.

[0035] The vapor detection and control schemes discussed above can be varied. For example, the system can detect the presence of substantial amounts of vapor at various levels within individual channels. In one such arrangement, the control system can detect the presence of vapor in individual spaces between pairs of opposed electrodes. In this arrangement, the control system may briefly deactivate the currently-used connection scheme. While the connection scheme is deactivated, the control system enters a vapordetection mode. It actuates switching circuit 52 to connect a single pair of opposed electrodes to opposite poles, determine the actual current between these electrodes and compare this actual current to an expected current for each pair. Here again, if the actual current is below the expected current by more than a current tolerance, this indicates that the space between the electrodes contains substantial amounts of vapor. By repeating this process for different pairs of electrodes, the system compiles data for the various spaces between pairs of electrodes indication whether or not each space has substantial vapor present. The control system may actuate the power supply 50 to supply a low voltage while in vapor detection mode, to avoid exceeding the maximum allowable current when testing individual pairs of electrodes. In this embodiment, the elevation data may include data identifying the position of each electrode in the current path. During normal operation, when the control system selects a new connection scheme, it avoids selection of any connection scheme which extends through an electrode bounding a space with vapor present.

[0036] The number of channels, number of electrodes and the configuration of the electrodes can be varied.

[0037] The invention has been described above with reference to a boiler. As used in this disclosure, the term “liquid heater” refers to a device which can heat the liquid, whether or not the device is adapted to boil the liquid. The term “heater” as used herein thus is inclusive of boilers and liquid heaters. Features discussed above also can be used in a liquid heater which does not boil the liquid. In particular, the electrode array, dielectric walls and switching circuit discussed above can provide numerous conductive paths of specific resistance spanning a wide range of specific resistances, and can be used in any liquid heater, without the need for the vapor detection features discussed above.

[0038] Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.