Patent Application
20200200488
The present invention relates to energy storage and in particular to heat storage. Specifically, a method and apparatus are disclosed for heat storage in combination with a pneumatic system in order to obtain high energy density.
With the continuous cost decline of solar and wind technologies, renewable power is becoming an increasingly competitive alternative to fossil-fuel based power (IRENA, 2018, Renewable Power Generation Costs in 2017, International Renewable Energy Agency, Abu Dhabi).
The increase in renewable power generation will allow effective carbon emissions reduction in key segments of the energy market. The electricity sector is undergoing a period of rapid change in the scale and breadth of renewable power generation technologies. At the end of 2016, total renewable power generation capacity surpassed 2000 GW, double the capacity of 2012 in a time window of 5 years.
In order for renewable power generation to grow to substantial levels, electricity systems will require great flexibility. This means electricity will need to be stored over days, weeks or months. Thus, energy storage will play a vital role in transforming the energy sector to high level shares of variable renewable generations in the near future. Bloomberg NEF (BNEF) estimates that the global energy storage market will grow to a cumulative 942GW/2857GWh by 2040, attracting $620 billion in investment over the next 22 years. This conclusion is consistent with the conclusion reached in the Electrification Future Study (EFS) (Hale, Elaine, Henry Horsey, Brandon Johnson, Matteo Muratori, Eric Wilson, et al. 2018. The Demand-side Grid (dsgrid) Model Documentation. Golden, Colo.: National Renewable Energy Laboratory. NREL/TP-6A20-71492).
Batteries are currently an active research direction for energy storage due to their many advantages, including high energy density and fast response. The main disadvantage of batteries, however, is short lifetime. Looking into the future, battery recycling may become a huge burden, which is an issue that is typically not included in the cost analysis.
Under the big picture of the Electrification Future Study (EFS) and the forecasted tremendous need for energy storage, heat and cold storage may also account for a large percentage of future energy storage. First, it is reported that HVAC accounts for 35% of total primary energy in the United States, and is expected to reach similar proportions in other countries (Michael Waite, Elliot Cohen, Henri Torbey, Michael Piccirilli, Yu Tian, Vijay Modi. Global trends in urban electricity demands for cooling and heating. Energy 2017: (127): 786-802). This means heat and cold storage can share a large proportion of the total energy storage market, even though the supply is currently dominated by fossil fuels, such as coal and gas. There is significant potential to upgrade existing systems and create new networks that are based on renewable energy sources, in which thermal storage will play a vital role. Second, it cheaper to store the electricity in the form of heat and cold energy for direct heating and cooling applications than to use battery storage. Third, the literature reports that the dynamical load control of refrigerators in a network achieves a significant delay in frequency-fall, thus reducing dependence on rapidly deployable backup generations (Joe A. Short, David G. Infield, and Leon L. Freries, Stabilization of grid frequency through dynamic demand control. IEEE transactions on power systems, 22(3):1284-1293, 2007).
This means HVAC systems with thermal storage capacity have great potential to be used as demand-side load management units for grid frequency stabilization. This may be of vital importance under the scenario of the large sharing of renewable power generation.
Energy storage is known in the art. See U.S. 2014/0109561, U.S. Pat. Nos. 7,832,207, and 9,482,109 each of which is incorporated by reference in its entirety.
Apparatus for heat storage, comprises a working fluid chamber for storing working fluid; a pressure support chamber coupled to the working fluid chamber and including pressure support material, said pressure support chamber for increasing pressure in said working fluid chamber responsive to compression of said pressure support chamber; a fluid pump for pumping working fluid into the working fluid chamber, wherein pumping fluid into the working fluid chamber increases pressure of said working fluid in the working fluid chamber; the pressure elevation of the working fluid in the fluid chamber is responsive to pumping the fluid back into the fluid chamber to compress the pressure support chamber; a working fluid chamber heat exchanger for varying temperature in said working fluid chamber; an output conduit for transferring working fluid from said fluid chamber to a utilization destination; and an input conduit for transferring said working fluid received from said utilization destination to said working fluid into the fluid chamber.
More specifically,
Vessel 15 can be formed in any shape, although a cylindrical shape is preferred for its inherent strength. The walls of vessel 15 may be formed of any material or thickness sufficient to contain the pressure levels generated within, although steel is preferred. The use of one or more layers of high tensile strength steel wire (or other materials such as carbon fiber) may be included as appropriate to further prevent sidewall rupture. End caps may optionally be reinforced with high-tensile rods. The interior of vessel 15 may have various linings (metal, ceramic, polymer, etc) to further prevent leakage. Vessel 15 may also be insulated.
Vessel 15 may be constructed with various safety features, including “leak before burst,” safety (or relief) valves, etc.
Working fluid chamber 10 is filled with a working fluid, e.g. a fluid such as water, and the fluid may be in a gas state, or a combination gas/liquid state. The temperature of the fluid is increased via second heat exchanger 80. Thus, this exchanger 80 (a working fluid chamber heat exchanger) is for varying temperature in said working fluid chamber. The heated fluid passes through valve 115 and travels via vapor conduit 90 (e.g. output conduit) as overheated vapor. The overheated vapor enters heat and work utilization units 18 where it is used for heating and/or energy production (i.e. a steam powered turbine).
Pressure support chamber 20 defines a void and may optionally include an elastic container that is comprises of elastic material. The elastic container may be, for example, a balloon or a tire that may be sealed and that encapsulates the void. Pressure support chamber may be filled (within optional elastic container if present) with pressure support material such as gas and/or liquid. In an exemplary embodiment, a refrigerant is included in pressure support chamber 20. Exemplary refrigerants include R134a, R422B, R414B and so on.
The pressure within the pressure support chamber can be managed through heating/cooling and/or pumping (via piston 30). Thus, first heat exchanger 60 is optionally included for changing the internal temperature of pressure support material in pressure support chamber 20. Thus, this heat exchanger may increase pressure in pressure support chamber 20 by heating the pressure support material. First heat exchanger 60 may receive heat charging via first heat charging source 40, cooling via cooling source 50 (a further cooling source) and/or further cooling via cooling conduit 65 (explained further below). Valves 115 are included for regulating flow of liquids for heating and/or cooling. Pump 95 is also included for regulating flow of liquid via cooling conduit 65.
After fluid releases heat energy within heat and work utilization units 18, cooled fluid exits units 18 and is collected within working fluid reservoir 35. An optional conduit allows fluid within working fluid reservoir 35 to be mixed with overheated vapor within vapor conduit 90 and reintroduced into heat and work utilization units 18. Thus, optional valve 115 is included for regulating flow of liquid between working fluid reservoir 35 and vapor conduit 90.
As working fluid chamber 10 needs to be refilled, a fluid transferor such as pump 95 and/or valve 115 is actuated to allow fluid to flow from working fluid reservoir 35 to working fluid chamber 10 via conduit 25. Thus, a fluid transferor transfers working fluid into working fluid chamber 10. Transferring fluid into working fluid chamber 10 increases pressure of the working fluid in the working fluid chamber. The pressure elevation of the working fluid in working fluid chamber 10 is responsive to transferring the fluid back into fluid chamber 10 to compress pressure support chamber 20. In some exemplary embodiments, conduit 25 allows first heat exchanger 60 to be bypassed.
Working fluid chamber 10 is intended to store temperature energy, while pressure support chamber 20 is intended to store pressure energy. In an exemplary embodiment of the present invention, when the working fluid in working fluid chamber 10 is pressurized at a high pressure level, the working fluid can be heated to a high temperature without concern of evaporation. Thus, a large temperature gradient of a working liquid can be obtained for sensible energy storage, which means high heat density. With the stored energy in the form of both pressure and temperature, this process can be referred to as enthalpy storage.
When the pressurized high temperature working fluid is released to a lower pressure environment (for example within heat and work utilization units 18), the working fluid is transformed from a liquid state to a gas state and the heat energy is carried by a vapor flow with high speed. This results in a high heat transfer rate and fast dynamical response, a feature lacking from other currently available methods of energy storage (such as molten salt, hot rocks or concrete, and PCMs).
The high energy density feature can be illustrated by the application of producing steam for space heating. A traditional water tank can only store hot water under 100° C., so its application is very limited. In an exemplary embodiment of the present invention, with water as the working fluid, water can be stored at a temperature much higher than 100° C. when it is under high pressure. When the water is released to an atmosphere environment, it becomes overheated vapor, and the vapor can be further used to vaporize more liquid water to produce low temperature steam for space heating (for example for a single house, a building or a district).
In one exemplary embodiment, pressure support chamber 20 for pressure support can just contain gas. In a further exemplary embodiment, first heat exchanger 60 is optional, as the enclosed gas can be compressed by pumping the working fluid from a reservoir back into the working fluid chamber 10, thus create high pressure for the working fluid in working fluid chamber 10. Pumping liquid is of higher efficiency than compressing gas directly, so it is a cost effective operation. The pressure of the gas in the pressure support chamber 20 can be further elevated through heating according to thermodynamic law.
To reduce or in some embodiments eliminate the use of pumping energy, one approach is the use of a suitable refrigerant or chemical substance in the gas chamber that can go through phase changes as a result of heating or cooling. To increase overall energy efficiency of heat storage apparatus 100, in one exemplary embodiment, working fluid may be stored in working fluid reservoir 35 after releasing energy in heat and work utilization units 18. When the working fluid is then pumped back into working fluid chamber 10 from reservoir 35, the working fluid first goes through heat exchanger unit 60, so that refrigerant, which may be selected based on the application temperature range, is cooled and is expected to change from gas to liquid. This results in pressure reduction in the pressure support chamber 20. In this manner, less pumping energy may be required to pump the working fluid back into pressure support chamber 20.
Thus, the working fluid received from units 18 is used to cool the pressure support material in the pressure support chamber via heat exchanger unit 60. The pressure in working fluid chamber 10 decreases responsive to the pressure support material in pressure support chamber 20 being cooled.
After cooling of the refrigerant, if the pressure in working fluid chamber 10 becomes lower than that in the reservoir, then the pump (and associated pumping energy) could be eliminated. Thus, the selection of refrigerant and/or potential chemical substance is performed to achieve a desirable pressure management purpose.
The above steps may be performed under microprocessor control. To summarize, in one exemplary embodiment of the present invention, the following steps may be performed:
In more detail,
With the discharge of the working fluid from working fluid chamber 10, the pressure energy in the system decreases and thus causes a continuous drop of the output pressure. If the final discharge pressure is greater than the saturation pressure of the working fluid being stored, the working fluid in working fluid chamber 10 will not vaporize and its temperature will remain at its initial stored point. Otherwise, partial working fluid will vaporize in working fluid chamber 10 to maintain working fluid chamber 10 at a saturation pressure that matches the temperature of the working fluid inside it. Usually, partial evaporation inside working fluid chamber 10 will not adversely impact operation of heat storage apparatus 100, but the temperature of the stored working fluid will experience some decrease due to the heat energy being used for evaporation. Whether this temperature drop is substantial and consequently falls short to meet the heat requirement by the application depends on the outlet pressure range between the initial and final states, as well as the initial temperature of the working fluid being stored.
Aiming to address the above issue, and also to bring out other operational benefits, an exemplary embodiment of the present invention relates to a strategy to realize constant pressure discharge. A constant discharge pressure means constant energy release, which is desirable in certain applications. An even more desired feature would be the amount of the energy being discharged could match with a variable demand. For this enthalpy storage process, pressure energy is a form of energy as important as the temperature energy. A higher output pressure means higher energy flow. A controllable output pressure for the working fluid can bring out the benefit of higher degree of freedom for operation.
To realize discharge pressure control, in one exemplary embodiment, an extra pressure source is provided. In this manner, controlled pressure release of working fluid from working fluid chamber 10 is realized by coupling pressure support chamber 20 with pressure supplementary vessel 210. As explained below, pressure in supplementary pressure vessel 210 is charged either by heating pressure support chamber 20 or by pumping working fluid into working fluid chamber 10 for compressing gas or refrigerant in pressure supplementary vessel 210.
As shown in
The heat supply for the downstream application can be specified by the pressure difference ΔP=P1−Pv1, which determines how much hot working fluid should be discharged. To meet a variable demand, Pv1 can be controlled through the valve opening. The purpose of the pressure supplementary vessel 210 is to maintain P1 at a constant value. Assume the following is a dynamic model for a system that implements a control algorithm:
P
1
=f(P2,Pv2,Ppump,qh)
where Ppump is the pumping energy gain by pumping the working fluid into chamber 214 of pressure supplementary vessel 210, which is a backup option. If the initial P2 is high enough to maintain P1 during the heat discharge process, then this extra pressure supply is optional. The same rationale applies to the option of pressure elevation by extra heat input qh. Thus, in this dynamical model, Pv2 is the main control variable, which determines the amount of gas to be released to enthalpy storage vessel 15, and Ppump, qh are the optional control variables for backup when P2 drops to a level that cannot maintain a constant P1.
As explained above, a single vessel with piston connected chambers is related to one exemplary embodiment of the present invention. There could be different variations of such an enthalpy storage system based on the configurations of the piston connected chambers or vessels, i.e., see
There are many other thermal energy storage technologies, such as sensible heat storage (hot rock or concrete, molten salt), latent heat storage (solid-to-liquid) and thermochemical heat storage. The most successful application is sensible heat storages. However, it suffers from low energy density. The liquid-to-solid phase change material (PCM) based latent heat storage suffers more challenges, such as low PCM conductivity, material deterioration under long term usage and potential equipment structure damage caused by density change during repeated cycles. To overcome those challenges, the cost of such a system usually is not low. A thermochemical heat storage system is still under research stage, which is more complicated and could be more expensive.
Compared to those common approaches, the present invention has several advantages. First, the storage system is simple and could be cost competitive. Second, due to discharging working fluid will be in a flow condition, a substantially high heat transfer coefficient can be obtained. Thus, this process is cost competitive and suitable for many applications.
By employing different working fluids and refrigerants, it may be possible to cover wide temperature and pressure ranges for different applications. Another advantage of this enthalpy storage process is that it can be used to transform heat to work. A further feature of this process is that it can be configured for large scale applications, as the CAES system is an example, which is usually for large scale applications.
Based on the selections of the working fluid and the refrigerant or the chemical substance, various exemplary embodiments of the present invention can have various applications as described below.
In one exemplary embodiment of the present invention, heat storage is used to produce steam for space heating. For this application, pressure support chamber 20 without a heating unit is used for illustration purposes as shown in
Under higher pressure, hot water can be stored at a temperature that is much higher than 100° C., thus resulting in a higher energy density. When hot water is released from the pressurized working fluid chamber 10 and into vapor conduit 90, it turns into overheated steam under a lower environment pressure. For domestic space heating, saturated steam around 100° C. under atmosphere pressure is sufficient. Thus, a stream of cold water from reservoir 35 can be drawn and mixed with the overheated vapor from vapor conduit 90 in mixer 91 to produce more steam for heating purpose. An exemplary structure with multiple sieves (like a distillation column) is illustrated in
To estimate the size feasibility of a pressurized vessel as depicted in
J=mC
p(Tmean−Ts)=905.9994 kWh/vessel,
where m is the total water mass in the vessel and Cp is its heat capacity.
Thus a vessel with values of the dimensions and parameters listed in Table 2 can provide heating steam for 3 modern houses with 300 m2 floor area each for 24 hours. So it can be concluded that the dimensions and pressure and temperature levels of the enthalpy storage process as shown in
Fast ramping for power generation is desirable due to the increased share of renewable power sources mingling into the grid. The enthalpy storage system can store high pressure and high temperature liquid water and be used to provide instant steam supply to increase the power supply for sudden excessive demand in the grid. When excessive electricity is being generated, hot steam can be drawn and used to charge the pressurized vessel, or electric heaters. The heating source can also come from solar thermal energy.
Many industrial processes require hot steam supply, desirable for intermittent heat sources. Thus the enthalpy storage process could be used to store water at a required high temperature and to provide hot steam for the industrial processes when needed.
In one exemplary embodiment of the present invention, the enthalpy storage process could be used in a concentrated solar power (CSP) plant for energy storage, to provide hot steam to generate electricity when the sun is not shining. Experience and technologies could be borrowed from a CASE system, which is usually for large scale applications, to support the configuration of the current enthalpy storage system. In this manner it is possible to store large amounts of water under high temperature and high pressure—to generate steam for power generation. Because the storage medium is the working fluid itself, the cost of this process could be lower than the use of current molten salt storage technology for a CSP plant.
Whereas many alterations and modifications of the disclosure will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular implementation shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various implementations are not intended to limit the scope of the claims, which in themselves recite only those features regarded as the disclosure.
This non-provisional application claims the benefit under 35 U.S.C. § 119(e) of U.S. Application Ser. No. 62/781,950 filed on Dec. 19, 2018 entitled “Enthalpy Storage System Based On Piston Connected Pressurized Vessels”, and whose entire disclosure is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 62781950 | Dec 2018 | US |
