Methods and systems for heating thermal storage units

1 . A thermal storage system for heating fluid flowing therethrough, the system comprising:

a thermal storage unit (TSU) having a first longitudinal axis;

insulation at least partially surrounding the TSU;

at least one flow channel disposed within the TSU;

an inlet in fluidic communication with the at least one flow channel, the inlet accepting the fluid to be heated;

an outlet in fluidic communication with the at least one flow channel;

a plurality of heaters, each of the plurality of heaters having a longitudinal centerline and a length, wherein the plurality of heaters are disposed at least partially within the TSU and each of the plurality of heaters are independently removable from the TSU; and

a controller for controlling electric power provided to the plurality of heaters.

2 . The system of claim 1 , wherein the plurality of heaters comprises a plurality of resistive cartridge heaters.

3 . The system of claim 1 , wherein the longitudinal centerline of each of the plurality of heaters is not parallel to the first longitudinal axis.

4 . The system of claim 3 , wherein the longitudinal centerline of each of the plurality of heaters is orthogonal to the first longitudinal axis.

5 . The system of claim 3 , wherein the longitudinal centerlines of the plurality of heaters form a single plane that is parallel to the first longitudinal axis.

6 . The system of claim 1 , wherein the at least one flow channel comprises at least two flow channels each having a channel centerline parallel to the first longitudinal axis, wherein the at least two flow channels are disposed next to each other and the plurality of heaters are disposed in between the at least two flow channels.

7 . The system of claim 1 , wherein the plurality of heaters are disposed to protrude externally out of the insulation.

8 . The system of claim 1 , wherein the plurality of heaters comprises one or more redundant heaters.

9 . The system of claim 1 , wherein at least two of the plurality of heaters are coupled in parallel to form a heater network, wherein the heater network is coupled to an electric power source.

10 . The system of claim 1 , further comprising a plurality of heater-fuse assemblies each having a fuse coupled in series with one of the plurality of heaters, wherein at least two of the plurality of heater-fuse assemblies are coupled in parallel to form a heater network.

11 . The system of claim 9 , further comprising a current sensor, wherein:

the current sensor is coupled to the heater network such that the current sensor detects current drawn by the heater network, and

the controller is programmed to adjust the electric power provided to the plurality of heaters responsive to signals from the current sensor.

12 . The system of claim 1 , further comprising a plurality of temperature sensors disposed to sense the temperature of the TSU at a plurality of locations, wherein the controller is programmed to require no more than a single temperature input signal to control the electric power provided to the plurality of heaters, wherein the single temperature input signal is equal to the average value of two or more of the temperatures sensed by the plurality of temperature sensors.

13 . The system of claim 12 , wherein the plurality of locations are a plurality of thermally equivalent locations.

14 . The system of claim 12 , further comprising a current sensor, wherein:

the current sensor is coupled to the plurality of heaters such that the current sensor detects current drawn by the plurality of heaters, and

the controller is programmed to adjust the electric power provided to the plurality of heaters responsive to signals from the current sensor.

15 . The system of claim 1 , further comprising:

a heater puller having proximal and distal ends, a coupler disposed on the distal end and an actuator disposed on the proximal end, wherein:

the coupler is configured to engage at least one of the plurality of heaters, and

the actuation of the actuator engages the coupler to at least one of the plurality of heaters.

16 . The system of claim 15 , further comprising a locking mechanism that prevents the coupler from disengaging from the at least one of the plurality of heaters.

17 . The system of claim 15 , wherein:

the coupler comprises a plurality of gripping surfaces to engage at least one of the plurality of heaters, and

the actuator comprises a plurality of handles and a pivot about which each one of the plurality of handles rotates, each one of the plurality of gripping surfaces coupled to one of the plurality of handles.

18 . The system of claim 15 , wherein:

the actuator comprises a sliding sleeve and a center rod slidably disposed within the sliding sleeve, the sliding sleeve having a distal sleeve end and the center rod having a distal rod end, and

the coupler comprises a ferrule disposed on the distal sleeve end, a plurality of compliant extensions disposed on the distal rod end, and grips mounted on the plurality of compliant extensions, the ferrule engaging the plurality of compliant extensions when the sliding sleeve is actuated in a distal direction with respect to the center rod.

19 . The system of claim 15 , wherein:

at least one of the plurality of heaters comprises at least one pin, and

the coupler comprises at least one L-shaped slot, the L-shaped slot configured to engage the at least one pin.

20 . The system of claim 15 , wherein:

at least one of the plurality of heaters comprises a loop, and

the coupler comprises a hook configured to engage the loop.

21 . The system of claim 15 , further comprising a protective housing having insulation, the protective housing having a longitudinal length equal to at least the length of each of the plurality of heaters.

22 . A backup energy system comprising:

the thermal storage system of claim 1 for heating fluid;

a turbine coupled to the thermal storage system for receiving the heated fluid from the outlet, the heated fluid driving the turbine; and

an electrical generator for providing electric power when the turbine is driven by the heated fluid.

23 . The backup energy system of claim 22 , wherein the fluid is compressed gas, the backup energy system further comprising a compressed gas system to provide the compressed gas to the thermal storage system.

24 . The backup energy system of claim 22 , further comprising at least one temperature sensor to sense the temperature of at least one component of the thermal storage system, wherein the controller is configured to reduce the electric power provided to the plurality of heaters when the temperature of the at least one component of the thermal storage system deviates from at least one acceptable temperature parameter that is related to parameters measured during a previous discharge event.

25 . A thermal storage system for heating fluid flowing therethrough, the system comprising:

a thermal storage unit (TSU) having a first longitudinal axis;

insulation at least partially surrounding the TSU;

at least one flow channel disposed within the TSU;

an inlet in fluidic communication with the at least one flow channel, the inlet accepting the fluid to be heated;

an outlet in fluidic communication with the at least one flow channel;

a plurality of heaters;

a controller for controlling electric power provided to the plurality of heaters; and

a plurality of heater-fuse assemblies each having a fuse coupled in series with one of the plurality of heaters, wherein at least two of the plurality of heater-fuse assemblies are coupled in parallel to form a heater network.

26 . The system of claim 25 , further comprising a current sensor, wherein:

the current sensor is coupled to the heater network such that the current sensor detects current drawn by the heater network, and

the controller is programmed to adjust the electric power provided to the plurality of heaters responsive to signals from the current sensor.

27 . A thermal storage system for heating fluid flowing therethrough, the system comprising:

a thermal storage unit (TSU) having a first longitudinal axis;

insulation at least partially surrounding the TSU;

at least one flow channel disposed within the TSU;

an inlet in fluidic communication with the at least one flow channel, the inlet accepting the fluid to be heated;

an outlet in fluidic communication with the at least one flow channel;

a plurality of heaters; and

a controller for controlling electric power provided to the plurality of heaters, wherein the controller is programmed to require no more than a single temperature input signal to control the electric power provided to the plurality of heaters.

28 . The system of claim 27 , further comprising a plurality of temperature sensors disposed to sense the temperature of the TSU at a plurality of thermally equivalent locations, wherein the single temperature input signal is equal to the average value of two or more of the temperatures sensed by the plurality of temperature sensors.

29 . The system of claim 27 , further comprising a current sensor, wherein:

the current sensor is coupled to the plurality of heaters such that the current sensor detects current drawn by the plurality of heaters, and

the controller is programmed to adjust the electric power provided to the plurality of heaters responsive to signals from the current sensor.

30 . A thermal storage system for heating fluid flowing therethrough, the system comprising:

a thermal storage unit (TSU) having a first longitudinal axis;

insulation at least partially surrounding the TSU;

at least one flow channel disposed within the TSU;

an inlet in fluidic communication with the at least one flow channel, the inlet accepting the fluid to be heated;

an outlet in fluidic communication with the at least one flow channel;

a plurality of heaters including at least one redundant heater; and

a controller for controlling electric power provided to the plurality of heaters.

31 . A method for heating fluid flowing through a thermal storage system, the method comprising:

providing a thermal storage unit (TSU) having at least one flow channel disposed therein;

providing a plurality of heaters disposed at least partially within the TSU;

controlling electric power provided to the plurality of heaters;

transferring heat from the plurality of heaters to the TSU from a plurality of locations within the TSU;

heating the TSU to a steady state temperature within a predetermined amount of time;

maintaining the TSU at the steady state temperature;

transferring heat from the TSU to the fluid flowing in the at least one flow channel; and

removing at least one of the plurality of heaters from the TSU without removing the remaining ones of the plurality of heaters from the TSU.

32 . The method of claim 31 , wherein providing a plurality of heaters comprises providing a plurality of resistive cartridge heaters.

33 . The method of claim 31 , wherein heating the TSU comprises heating the TSU to the steady state temperature within the predetermined amount of time even when one of the plurality of heaters fails.

34 . The method of claim 31 , wherein controlling electric power further comprises requiring no more than a single temperature input signal to control the electric power provided to the plurality of heaters.

35 . The method of claim 34 , further comprising sensing current drawn by the plurality of heaters, wherein controlling electric power further comprises controlling electric power provided to the plurality of heaters responsive to the sensed current.

36 . The method of claim 31 , further comprising removing at least one of the plurality of heaters from the TSU while the temperature of the TSU is substantially equal to the steady state temperature.

37 . The method of claim 31 , wherein controlling electric power comprises controlling electric power provided to the plurality of heaters using a DC voltage control algorithm.

38 . The method of claim 31 , wherein controlling electric power comprises controlling electric power provided to the plurality of heaters using a variable time-base zero-crossing control algorithm.