Thermal storage and supply

Abstract

There is disclosed a thermal energy storage and supply method that includes providing subcooled water to a pressure vessel; heating liquid water within the pressure vessel using an electrically-powered heater so that the vessel contains saturated liquid water and steam at a variable storage pressure; controlling the heater to raise the storage pressure to a peak storage pressure of at least 2 MPa; and selectively discharging steam from an outlet of the pressure vessel to a thermal load, in response to a thermal energy demand, such that during a depletion period the storage pressure reduces by at least 1 MPa from the peak storage pressure.

1 . A method of thermal energy storage and supply, comprising:
 providing subcooled water to a pressure vessel;   heating liquid water within the pressure vessel using an electrically-powered heater so that the vessel contains saturated liquid water and steam at a variable storage pressure; controlling the heater to raise the storage pressure to a peak storage pressure of at least 2 MPa; selectively discharging steam from an outlet of the pressure vessel to a thermal load, in response to a thermal energy demand, such that during a depletion period the storage pressure reduces by at least 1 MPa from the peak storage pressure.   
     
     
         2 . A method according to  claim 1 , wherein:
 the discharged steam is provided to the thermal load directly without passing through an intermediate steam accumulator; or   any steam accumulator or steam accumulators between the pressure vessel and the thermal load have a total volume which is less than a volume of the pressure vessel.   
     
     
         3 - 5 . (canceled) 
     
     
         6 . A method according to  claim 1 , wherein steam is discharged to the thermal load at a discharge pressure;
 wherein subcooled water is provided to the vessel when the storage pressure is greater than the discharge pressure; and   wherein the subcooled water is provided to the pressure vessel during the depletion period.   
     
     
         7 - 14 . (canceled) 
     
     
         15 . A method according to  claim 1 , wherein there is a plurality of thermal loads including a first thermal load and a second thermal load;
 wherein steam is selectively discharged from the pressure vessel to each of the thermal loads via respective control valves, based on respective thermal energy demands;   wherein a flash potential corresponds to an amount of steam that can be flashed from liquid water within the pressure vessel before the storage pressure reaches a lower limit pressure for sustaining discharge of steam to the thermal load; the method further comprising:   evaluating a criterion corresponding to whether the flash potential is sufficient to meet a predicted demand of the plurality of loads;   based on the evaluation and on priority data relating to the thermal loads, determining to discharge steam to the first thermal load to meet a respective first thermal energy demand in preference to discharging steam to the second thermal load to meet a respective second thermal energy demand.   
     
     
         16 . A method according to  claim 1  comprising, during a recharge period:
 heating liquid in the pressure vessel to raise the storage pressure by at least 1 MPa to a peak storage pressure of at least 2 MPa; 
 providing subcooled water to the pressure vessel to reach a peak mass of water in the pressure vessel corresponding to a peak liquid level at the peak storage pressure; and 
 phasing a profile of water supply during the recharge period so that it is front-loaded relative to a profile of heating during the recharge period. 
 
     
     
         17 . (canceled) 
     
     
         18 . A method according to  claim 16 , wherein a flash potential corresponds to an amount of steam that can be flashed from liquid water within the pressure vessel before the storage pressure reaches a lower limit pressure for sustaining discharge of steam to the thermal load; and
 wherein a liquid level margin corresponds to an amount of liquid water within the pressure vessel above a lower limit amount for operation of the heater upon discharge of the flash potential;   wherein the method comprises, during a water-priority portion of the recharge period, phasing a profile of water supply relative to a profile of heating to maintain a minimum recharge flash potential while increasing an amount of water within the pressure vessel to the target peak mass of water, such that the liquid level margin progressively rises; and   subsequently heating the liquid water during a flash-priority portion of the recharge period to raise the storage pressure to the peak storage pressure.   
     
     
         19 - 24 . (canceled) 
     
     
         25 . A method according to  claim 1 , comprising a recharge period in which liquid in the pressure vessel is heated to raise the storage pressure by at least 1 MPa to a peak storage pressure of at least 2 MPa;
 wherein a dimensional ratio of (i) the cumulative enthalpy of (i) steam discharged from the pressure vessel during the depletion period and (ii) an average reheat power of the heater during the recharge period is at least 25000 seconds; wherein the average reheat power is defined as a cumulative energy provided to the liquid water during the recharge period, divided by a duration of the recharge period.   
     
     
         26 . (canceled) 
     
     
         27 . A thermal energy storage and supply installation comprising:
 a pressure vessel for storing water comprising saturated liquid water and steam at a storage pressure of 2 MPa, the pressure vessel having an outlet to discharge steam to a thermal load;   an electrically-powered heater configured to heat liquid water stored in the pressure vessel to vary a storage pressure within the pressure vessel;   a controller configured to operate the thermal storage installation by:   controlling the heater to heat liquid water within the pressure vessel to reach a peak storage pressure of saturated liquid water and steam of at least 2 MPa;   controlling a control valve to selectively discharge steam from the outlet to a thermal load, in response to a thermal energy demand;   permitting steam discharge to meet the thermal energy demand so that the storage pressure reduces by at least 1 MPa from the peak storage pressure.   
     
     
         28 - 32 . (canceled) 
     
     
         33 . An installation according to  claim 27 , further comprising a subcooled water supply vessel configured to store subcooled water for supply to the pressure vessel;
 wherein a ratio of a storage volume of the subcooled water supply vessel to a storage volume of the pressure vessel is at least 5%.   
     
     
         34 . An installation according to  claim 27 , wherein the controller is configured to selectively operate in an extended depletion mode in which the controller permits steam to be discharged so that a liquid level of liquid water within the pressure vessel falls below a lower limit liquid level for operation of the heater during the depletion period, wherein the controller prevents heating with the heater when the liquid level is below the lower limit liquid level for operation of the heater. 
     
     
         35 . An installation according to  claim 27 , wherein the thermal load comprises a heat exchanger oriented with respect to the pressure vessel to define a thermosiphon between the pressure vessel and the heat exchanger, whereby discharged steam condensing within the heat exchanger forms a column of subcooled water that is returned to a condensate inlet at a lower portion of the pressure vessel. 
     
     
         36 . An installation according to  claim 35 , wherein the heat exchanger is disposed at a higher position than the pressure vessel and the controller is configured to cause steam to be discharged to the heat exchanger at a discharge pressure selected such that, given the relative position of the heat exchanger, there is adequate head to return the subcooled water to the pressure vessel under the action of gravity; and/or
 wherein the controller is configured to control heat exchange at the heat exchanger such that the water is subcooled by at least 10° C.   
     
     
         37 . (canceled) 
     
     
         38 . An installation according to  claim 27 , wherein a flash potential corresponds to an amount of steam that can be flashed from liquid water within the pressure vessel before the storage pressure reaches a lower limit pressure for sustaining discharge of steam to the thermal load; and
 wherein a liquid level margin corresponds to an amount of liquid water within the pressure vessel above a lower limit amount for operation of the heater upon discharge of the flash potential;   wherein the controller is configured to select between operating the thermal storage installation in a recharge mode or a depletion mode based on a predetermined setting such as a time-dependent setting, based on a user input, or based on a predicted demand profile and/or a predicted power output profile of the heater;   wherein in the depletion mode, the controller is configured to evaluate a criterion corresponding to whether the liquid level margin is positive or negative; and to provide subcooled water to the pressure vessel to increase the liquid level margin and reduce the flash potential when the evaluation corresponds to the liquid level margin being negative; and/or   wherein in the recharge mode, the controller is configured to phase a profile of water supply relative to a profile of heating to (i) maintain a minimum recharge flash potential which is a predetermined flash potential or which corresponds to a predicted demand, while a liquid level margin and an amount of water in the pressure vessel progressively increases to a target mass of water corresponding to a target liquid level at the peak storage pressure; and (ii) subsequently heat the liquid water to raise the storage pressure to the peak storage pressure.   
     
     
         39 - 40 . (canceled) 
     
     
         41 . An installation according to  claim 38 , wherein in the recharge mode, the controller is configured so that when the predicted demand corresponds to no demand for steam during an idle portion of a recharge period, the controller causes subcooled water to be supplied to reduce the storage pressure below the lower limit pressure during the idle portion. 
     
     
         42 . (canceled) 
     
     
         43 . An installation according to  claim 27 , wherein the pressure vessel is configured to discharge steam to a plurality of thermal loads via respective control valves, including a first thermal load and a second thermal load;
 wherein the controller is configured to evaluate a criterion corresponding to whether the flash potential is sufficient to meet a predicted demand of the plurality of loads;   wherein, responsive to an outcome of the evaluation, the controller is configured to evaluate priority data specifying relative priorities of the thermal loads, and to operate in a priority discharge mode in which it controls selective discharge of steam to meet a thermal energy demand of a relatively high priority thermal load in preference to controlling selective discharge of steam to meet a thermal energy demand of a relatively lower priority thermal load.   
     
     
         44 . An installation according to  claim 27 , configured to provide water in the form of steam discharged from the pressure vessel to the thermal load in an open arrangement, by which the thermal load consumes the water provided as steam without corresponding return of the water as condensate; and
 wherein the controller is configured to discharge steam to the thermal load at a minimum discharge pressure of between 0.5 MPa and 1.0 MPa, or the thermal load is configured to receive discharged steam at a minimum discharge pressure of between 0.5 MPa and 1.0 MPa.   
     
     
         45 . An installation according to  claim 27 , configured to supply steam discharged from the pressure vessel to at least two thermal loads; wherein:
 the thermal storage installation is configured to provide water in the form of steam discharged from the pressure vessel to one of the thermal loads in an open arrangement, by which the water is placed into contact with a foreign process fluid or article, and/or is discharged from the thermal load without corresponding return of the water as condensate; and   the thermal storage installation is configured to provide water in the form of steam discharged from the pressure vessel to one of the thermal loads in a closed loop, by which the water is at least partly returned to the pressure vessel as subcooled water, for example via a subcooled supply vessel.   
     
     
         46 . An installation according to  claim 27 , wherein the pressure vessel is provided with a deaerator configured to receive an inlet flow of subcooled water along a deaeration path, and configured to direct a deaerating flow of steam from within the pressure vessel in counterflow along the deaeration path;
 wherein the controller is configured to vary a velocity of the deaerating flow of steam as a function of a temperature of the inlet flow and/or a temperature of the steam, to target the inlet flow reaching a saturation temperature corresponding to the steam along the deaeration path, over a range of storage pressures.   
     
     
         47 . An installation according to  claim 27 , wherein the heater is installed within the pressure vessel so that a lower limit liquid level for operation of the heater corresponds to a liquid fraction of water within the pressure vessel of no more than 60%.