CO2 emissions from the transportation sector comprise a significant portion of total greenhouse gas emissions. Although CO2-neutral options including battery electric vehicles and hydrogen fuel cell vehicles are being introduced, significant issues remain especially related to storage energy density and specific energy, cost, and infrastructure requirements. Hydrocarbon fuels are also a possibility assuming that they are produced from a renewable energy source, such as biogasification or electrolysis driven by wind or solar electricity. Hydrocarbons have a significant advantage in that they have much higher energy density than compressed H2 or lithium-ion batteries. However, even in scenarios where a renewably-produced hydrocarbon fuel is utilized, the resulting CO2 product is released into the atmosphere. While CO2 removal from the atmosphere for use in the further production of renewable hydrocarbon fuel is possible, atmospheric extraction introduces considerable additional complexity, cost, and energy loss due to the relatively low CO2 concentration.
In one aspect, a motorized vehicle is provided, the vehicle comprising a device configured to convert a fuel comprising a hydrocarbon, an alcohol, or both, to an exhaust comprising CO2, and a tank configured to store, under pressure, the exhaust comprising CO2 and an inlet port configured to receive the exhaust from the device. In embodiments, the device is a solid oxide fuel cell (SOFC). In embodiments, the tank is a co-storage tank configured to store, under pressure, the fuel comprising the hydrocarbon, the alcohol, or both, and the exhaust comprising CO2, the co-storage tank further comprising an outlet port configured to deliver the fuel to the device. Methods of using the motorized vehicle are also provided.
Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.
Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.
Provided are energy storage systems, components of such systems, and related methods. The systems may be characterized as being CO2-neutral and in illustrative embodiments, CO2-negative. The energy storage systems may be used to store CO2-containing exhaust in a variety of types of motorized vehicles and in embodiments, to co-store both the exhaust and a fuel to power the motorized vehicle.
Co-Storage Tanks and Energy Storage Systems
In embodiments, energy storage systems are provided which are based on storing both fuel and exhaust comprising CO2 in a single tank. An illustrative embodiment of a co-storage tank 100 is shown in
Chamber volumes and pressures, both of which determine suitable sizes for the chambers 106a, 106b, and thus, overall tank 100 size, are described further below. Since the inventors have determined that fuel and CO2 volumes are similar for most fuels, dual-chamber, co-storage tanks such as tank 100 significantly reduce total tank volume and also cost. Besides minimizing CO2 emission, this on-board capture approach also has substantially lower cost compared to atmospheric capture of CO2.
To achieve reasonable co-storage tank volumes, the fuel stored therein is reacted with pure oxygen rather than air. This prevents CO2 from being diluted with large amounts of N2. To achieve this,
As also described below, co-storage tank sizes are found to be within a factor of two of common liquid hydrocarbon fuels (gasoline, diesel). Tank sizes are even more comparable given the higher SOFC conversion efficiency compared to existing internal combustion heat engines, such that less fuel is required for a given distance traveled. Moreover, a key advantage compared to hydrogen fuel cells is that the present co-storage tank is about 3 times smaller compared to hydrogen tanks and the pressure needed and energy required for compression is much reduced. In addition, although the mass of the stored CO2 product is 2-3 times greater than that of the fuel, the mass is still much reduced compared to battery electric vehicles.
Fuel and Exhaust Storage Volume/Mass
The volume required for fuel/exhaust co-storage is assessed based on the densities and properties of these gases/liquids at elevated pressure. First, the properties of compressed CO2 are considered to estimate the volume required for storing captured exhaust comprising CO2. (See
The present co-storage tanks, such as tank 100, may be used to store various fuels including hydrocarbons (e.g., methane, propane, gasoline) and alcohols (e.g. ethanol, methanol). Biogas is another fuel that may be used. Except for methane, most common fuels are liquid or become liquefied at elevated pressure. Thus, except for methane, the stored fuel may be in its liquid form. As further described below, SOFCs are the most fuel-flexible type of fuel cell, but external fuel reforming may be required prior to introduction into the SOFC, particularly for higher C-number molecules (e.g. gasoline or diesel). Such a reformer may be included in any of the disclosed energy storage systems. As also further described below, different fuels have different practical advantages (e.g., reforming requirements, handling characteristics of liquid versus gaseous, existing fuel infrastructure) and also slightly different required storage volumes. Together with local availability and cost, these factors will guide selection of the type of fuel to be used.
In order to evaluate the fuel and CO2 storage volumes, specific fuels are considered in detail below, including methane, gasoline, and ethanol.
Methane: Methane is relatively simple to produce from renewable sources (e.g. from electrolytically-produced hydrogen). Another advantage of methane is that fuel processing for use in SOFCs is relatively simple.
The CH4 oxidation reaction is:
CH4+2O2→2H2O+CO2. ΔH=−810 kJ (1)
Assuming that the fuel is pure CH4, the oxidant is pure oxygen, and that it is completely combusted the only species in the exhaust are H2O and CO2 (in reality, the combustion is not complete and low levels of impurities such as H2 and CO will also be present in the exhaust, as further described below.) The number of moles of CH4 reactant and CO2 product in equation (1) are the same. When the products are cooled from SOFC operating temperature (600° C.-800° C.) to near ambient temperature, the H2O is separated as liquid, leaving concentrated CO2. Thus, for every mole of CH4 consumed, a mole of CO2 is produced, supporting the feasibility of using a single tank to store both CH4 and CO2. As shown in
Assuming that the CO2 is compressed to 700 bar just above the critical temperature for CO2, where the density in
Gasoline: Since gasoline consists of a range of different hydrocarbons, for simplicity, a typical one is considered, iso-octane. The oxidation reaction is:
C8H18+(12.5)O2→9H2O+8CO2, ΔH=−5.46 MJ (2)
The fuel is liquid with a density of 735 g/l (6.44 mol/l) at 700 bar and 706 g/l (6.18 mol/l) at 250 bar. The fuel volume is 30.7 l/GJ at 700 bar and 31.9 l/GJ at 250 bar. The C/H ratio is higher than for CH4, and hence the amount of CO2 is greater, leading to a value of 65.2 l/GJ at 700 bar and 75.7 l/GJ at 250 bar. Thus, in this case, the size of the co-storage tank 100 is dictated by CO2, requiring approximately double the volume as compared to gasoline. Similar results are obtained for other common transportation fuels such as diesel and jet fuel.
Ethanol: The ethanol oxidation reaction is:
C2H5OH+3O2→3H2O+2CO2, ΔH=−1.368 MJ (3)
Ethanol is liquid with a density of 780 g/l (17.1 mol/l) that varies little with pressure. The fuel volume is 45.0l/GJ versus 66.9l/GJ for CO2 at 700 bar, or 46.6l/GJ versus 77.7l/GJ for CO2 at 250 bar. In this case, CO2 dictates the size of the co-storage tank 100.
As shown in
For a given fuel energy, the co-storage tank 100 is approximately twice the size of existing fuel tanks in internal combustion engine vehicles. However, considering the greater fuel efficiency of SOFCs (in combination with electric motors) as compared to internal combustion engine vehicles, the co-storage tank 100 is closer to about 1.25 times the size of such existing fuel tanks.
As shown in
Vehicles Incorporating the Energy Storage Systems
The present co-storage tanks (including co-storage tank 100) and energy storage systems (including energy storage system 200) may be used in various applications, including as part of an energy conversion system in a motorized vehicle. This is illustrated with reference to
The energy storage system 500 further comprises the co-storage tank 510 in addition to the SOFC 508. Similar to the tank 100 of
The SOFC 508 is a stack of individual SOFCs, each comprising an anode, a cathode, and a solid electrolyte separating the anode and the cathode. A variety of designs may be used for the SOFC 508 (i.e., various configurations, compositions, components), provided the design allows the SOFC to convert the fuel into CO2. The SOFC 508 has an anode inlet port 516a in fluid communication with the first chamber 514a so as to receive the fuel and an anode outlet port 516b in fluid communication with the second chamber 514b so as to release exhaust comprising CO2 therein. The SOFC 508 has a cathode inlet port 517 in fluid communication with a source of O2 (e.g., air).
The SOFC 508 may be maintained at high temperature (e.g. 600-850° C.) and atmospheric pressure. Thus, as shown in
Notably, aside from the removal of water via the cooler 522, the exhaust released from the SOFC 508 is directly stored on-board the vehicle 503 via the tank 510. As noted above, this exhaust generally comprises other impurities such as H2 and CO. Neither the energy storage system 500, the hybrid battery system 502, or the vehicle 503 comprises an oxygen generator to produce O2 or a burner or other device to process the exhaust by reacting it with either air or O2 (from the oxygen generator) to remove such impurities. This is advantageous as it reduces complexity, avoids introducing N2, and increases efficiency.
The SOFC 508 provides a source of power which may be connected to an electrical load. As shown in
During use, when the fuel in the first chamber 514a of the tank 510 is mostly (or completely) depleted and the second chamber 514b of the tank 510 is mostly (or completely) filled, the system 500 can be re-fueled at a station providing a source of fuel (e.g., high pressure CH4) The station may also have the ability to off-load the captured CO2 for storage or use in further conversion to renewable fuel using some type of renewably-powered electrolysis technology.
For example, an illustrative embodiment showing an energy storage system 600 operatively connected to a fuel filling station is shown in
It is to be understood that the energy storage systems 200, 500 and 600 may each comprise fewer, additional, and/or different components as compared to those illustrated in the respective figures. Boxes grouping and separating system components (see e.g.,
Methods of using the present co-storage tanks and energy storage systems are also provided. Illustrative embodiments of such a method can comprise filling the co-storage tank (or an appropriate chamber thereof) with a fuel (e.g., a fuel comprising CH4). The fuel can be from a renewable source (e.g., from an electrolysis/catalysis system as described above) or a non-renewable source. At this stage, the co-storage tank may not comprise any exhaust (or an appropriate chamber thereof may be empty). Whenever power is needed, the method can comprise introducing O2 (the source of which may be air) into the cathode inlet port of the SOFC and introducing the fuel into the anode inlet port of the SOFC under conditions (e.g., at an appropriate temperature) to convert the fuel into CO2 and generate electricity. The CO2 exits the SOFC as exhaust which is captured/stored in the co-storage tank (or an appropriate chamber thereof). As noted above, the method need not comprise generating any O2 and/or processing the exhaust (e.g., via a burner) prior to storage. The conversion of fuel to exhaust/CO2 can continue until the co-storage tank is empty of fuel. To release CO2 from co-storage tank, the CO2 can technically be released into the atmosphere. However, as described above, the co-storage tank is desirable so that CO2 can be offloaded for storage or coupled to an electrolysis/catalysis system configured to convert the CO2 into a renewable fuel. This renewable fuel can then be used to refill the co-storage tank. Variations are contemplated involving the use of separate tanks instead of the co-storage tanks.
In embodiments, an energy storage system is provided, the system comprising: a co-storage tank configured to store, under pressure, a fuel comprising a hydrocarbon, an alcohol, or both, and an exhaust comprising CO2, the co-storage tank comprising an outlet port configured to deliver the fuel and an inlet port configured to receive the exhaust; and a SOFC configured to convert the fuel into the exhaust comprising CO2, the SOFC comprising an anode inlet port configured to connect to the outlet port of the co-storage tank to receive the fuel and an anode outlet port configured to connect to the inlet port of the co-storage tank to release the exhaust.
In embodiments, a co-storage tank for co-storage of a fuel and CO2 is provided, the tank comprising: walls configured to store, under pressure, a fuel comprising a hydrocarbon, an alcohol, or both, and an exhaust comprising CO2; an outlet port configured to deliver the fuel to a SOFC configured to convert the fuel into the exhaust comprising CO2; and an inlet port configured to receive the exhaust from the SOFC. The co-storage tank of claim 19, further comprising a partition that separates the co-storage tank into a first chamber for the fuel and a second chamber for the exhaust. The co-storage tank of claim 20, wherein the partition is self-adjustable. The co-storage tank of claim 19, wherein the fuel comprises CH4.
It is noted that any of disclosed energy storage systems may be in the form of a module that may be operatively connected to a vehicle, e.g. as a trailer or pod, as desired, e.g., when longer range is needed. For example, any of the disclosed energy storage systems may be configured as a self-contained component that can be attached or removed from a vehicle, e.g., depending on the vehicle range required. Such embodiments are particularly useful for battery electric vehicles configured for short range trips and having a small inexpensive light-weight battery. When going on a longer trip, a user may simply stop at a fueling station, but instead of just fueling, any of the disclosed energy storage systems may be rented and attached via an electrical umbilical (and then returned at the end of the trip).
Additional description of the vehicular applications of the present co-storage tanks and energy storage systems and comparison to existing technologies such as hydrogen and lithium ion batteries are found in U.S. Applications Nos. 62/882,775 and 62/940,316, each of which is incorporated by reference.
The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more.”
The foregoing description of illustrative embodiments of the disclosure has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principles of the disclosure and as practical applications of the disclosure to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents.
The present application claims priority to U.S. provisional patent application No. 62/882,775 that was filed Aug. 5, 2019, and U.S. provisional patent application No. 62/940,316 that was filed Nov. 26, 2019, the entire contents of both of which are incorporated herein by reference.
This invention was made with government support under DE-SC0016965 awarded by the Department of Energy and under 1545907 awarded by the National Science Foundation. The government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US20/44838 | 8/4/2020 | WO |
Number | Date | Country | |
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62882775 | Aug 2019 | US | |
62940316 | Nov 2019 | US |