Abstract
This invention relates to a unique cycle for generating electricity at high efficiency and with zero carbon emissions. The cycle's fundamental energy carrier is hydrogen (H2), with H2 undergoing each unit process in the cycle either within water (H2O) molecules or as H2 gas. The heat source driving the cycle, through generation of steam, is a small nuclear reactor known in the industry as a small modular reactor (SMR). This steam's primary purpose is to provide the feed source for H2 production, which occurs in an Underground Coal Gasifier (UCG). The invention's high generation efficiency, accompanied by zero carbon emissions, derive from the UCG's steam/coal reactions and from conversion of the H2 into electricity by solid oxide fuel cells (SOFCs). These SOFCs produce, as their only waste stream, pure H2O. This H2O is then fed back for steam generation using the SMR's heat, which re-initiates the cycle. All unit processes use proven, commercially available technologies. The invention is directly applicable to any location where significant coal deposits exist.
Claims
1) An H2 cycle for producing electricity with no accompanying carbon emissions, comprising a small modular nuclear reactor (SMR) as a heat source to drive the cycle, a Steam Generator to phase change water to steam using heat from the SMR, an Underground Coal Gasifier (UCG) to react this steam with in-situ coal to generate H2, a Solid Oxide Fuel Cells (SOFCs) to generate electricity using the UCG-produced H2 as a fuel, and a recycle of the SOFCs' byproduct H2O back to the steam generator to repeat the cycle. Said cycle uses H2 as its working element, alternately either as H2 gas or as H2O throughout the cycle, with said cycle consisting of these SMR, UCG, SOFC and steam generation processes.
2) The process of claim 1 wherein SMR rated output may provide anywhere between 1 MW and 1000 MW for steam generation, and wherein the Steam Generator's output steam may be at any temperature and pressure combination.
3) The process of claim 2, wherein reaction of steam and O2 with coal in the UCG occurs with the feed stream supplied at a steam: O2 ratio of 12 (+/?2).
4) The process of claim 2, wherein the first stage of the UCG is maintained at between 1000? C. and 1200? C. through controlled oxidation of the coal at the initial contact area of the feed stream with the UCG.
5) The process of claim 2, wherein the UCG's coal-gasifying conditions occur in a range between 1 and 100 atmospheres of pressure.
6) The process of claim 5, wherein resulting H2 gas is combined with O2 extracted from ambient air in SOFCs, and wherein these SOFCs have rated output between 1 and 1000 MW in total, at output AC voltages compatible with commercially available step-up transformers that may step up the SOFCs' output voltage for supply to a Transmission Grid.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] A clear understanding of the key features of the invention may be aided by reference to the appended drawings, which illustrate the method and system of the invention. These drawings depict preferred embodiments of the invention, but are not to be considered as limiting its scope with regard to other benefits which the invention is capable of achieving. Accordingly:
[0018] FIG. 1 provides an OLIVIA System Layout Diagram.
[0019] FIG. 2 provides an OLIVIA Process Flow Diagram.
[0020] FIG. 3 provides an OLIVIA Energy Flow Diagram.
DETAILED DESCRIPTION
[0021] FIG. 1 depicts the OLIVIA System Layout, with the major components described as follows. The SMR 1 serves as the process' driving heat source, with zero carbon emissions. A Steam Generator 2 adds SMR heat to H2O returned from the SOFCs, in order to generate steam. The Injection Well Head 3 delivers O2 and H2O (as steam) to the coal seam. The UCG 4 consists of a volumetric area in the coal seam where coal gases are produced. The Production Well Head 5 withdraws and separates coal gas into its H2, CH4, CO2 and CO components. SOFCs 6 efficiently produce carbon-free electricity, with pure H2O as their only waste byproduct. The SOFCs' output power, nominally at 10 kV to 20 kV but not limited to this range, has its voltage stepped up in transformers so that the power may be then supplied to a Transmission Grid 7. Nominally 4% of the coal gas volume consists of CH4, and this marketable CH4 is separated and stored for distribution 8. The CO2 and CO separated from the coal gas, 25% and 6% of coal gas by volume respectively, are captured and processed for deep storage 9.
[0022] FIG. 2 describes the Process Flows, maintaining the same numbering scheme as FIG. 1. The SMR 1 may use either water or air as a medium for providing heat to the Steam Generator. As a key feature of the invention, the Steam Generator produces steam that is used solely to generate coal gas in the UCG 4. In addition to conveying this steam, the Injection Well Head 3 also delivers O2 from a commercially available oxygen separation unit. This O2 is supplied for the partial oxidation of coal in Zone I of the UCG in order to establish the desired process temperature band of 1000 C to 1200 C for Zone I of the UCG. The UCG produces H2 gas from its three inputs: steam, O2 and the Coal Seam's carbon. The chemical reactions occur within three sequential UCG zones. Zone I partially oxidizes Coal in order to establish the desired process temperature, according to the Zone I reaction: C+O2.fwdarw.CO2+Heat. In Zone II, Coal and CO2 react to convert the CO2 to CO according to the Zone II reaction: C+CO2+Heat.fwdarw.2CO. Also in Zone II, Coal and Steam react to Generate H2 according to the Zone II reaction: C+H20+Heat.fwdarw.CO+H2. Zone III's Water Gas Shift Reaction (WGSR) then produces additional H2 according to the Zone III reaction: CO+H20+Heat.fwdarw.CO2+H2. By solving these equations' reaction rates, using standard equilibrium constants and assuming a steam:O2 feed ratio of 12:1, these Coal Gas volume fractions result: 65% H2, 25% CO2, 6% CO, and 4% CH4. These are nominal volume fractions, and actual fractions may vary depending on site-specific conditions. Separation of coal gas into its components occurs at the Recovery Well Head 5. Coal Gas is first cooled, then separated 8 into H2 and CH4 products, before capturing CO2 and CO in order to process them for deep storage 9. All of these unit processes are accomplished using proven, commercial-off-the-shelf technologies. The oxidation and reduction reactions within SOFCs are a proven and commercially available technology for generation of electricity 6, although to date SOFCs have yet to enjoy mass production. Their nominal efficiencies result in conversion of 47% of H2's lower heating value (LHV) into electricity. Aside from H2, the only other input is ambient air which provides the O2 source that SOFCs require in order to function. Once the SOFCs have converted these H2 and O2 inputs into MWs for the Grid, their only waste stream is H2O that contains recoverable heat. This H2O is then returned to the Steam Generators 2, where SMR heat will convert the H2O to steam and thus allowing the OL VIA cycle to repeat.
[0023] FIG. 3 is the OLIVIA Energy Flow Diagram, and it demonstrates the amount of electrical energy the OLIVIA Cycle can generate, relative to a given heat input (again, using same numbering scheme as FIG. 1). For modeling purposes, this specification assumes that the SMR 1 inputs 150 MW of heat to the process, which is a typical capacity rating for a commercially available SMR. As the OLIVIA cycle may use any heat input rating between 1 and 1000 MW, with the scaled results remaining identical to this 150 MW example, 150 MW is selected solely to illustrate the energy flows and loads throughout the OLIVIA cycle. Energy losses throughout the cycle are typical for the efficiency of each component. For example, the Steam Generator 2 is assumed to transfer 95% of the SMR heat to the water being converted to steam. The SOFCs 6 are assumed to convert 47% of the LHV of the H2 supplied to them into electricity. This is a typical value for SOFCs. Similarly, it is conservatively assumed that 22% of the SOFCs' waste heat may be recovered within the byproduct water that is returned in the cycle to the Steam Generator. The Energy Flow Diagram illustrates the key to the OLIVIA Cycle's capability to serve as an energy multiplier. When, in this typical example, 218 MW of steam are supplied to the UCG 4, the strongly endothermic steam/coal reactions go to work and provide OLIVIA's energy multiplier. The actual numbers are straightforward: balancing the chemical equations, the UCG's H2.sub.out/H20.sub.in molar ratio is equal to 1. Since steam has 21 kBTU/lb-mol and H2 has 104 kBTU/lb-mol, then mole for mole H2 has roughly 5 times the heating value of H20. Derating for efficiencies, we conservatively assume that only 80% of the coal seam is contacted/reacted with the steam and that only 75% of this contacted coal is carbon by weight. The result: 218 MW of steam converts to 680 MW of H2 lower heating value (LHV). Applying the SOFCs' 47% conversion efficiency to the 680 MW of H2 supplied, this results in 320 MW.sub.elec of electricity. A conservative 20 MW is assumed for powering the cycle's components, the two largest internal loads being an O2 separation unit for the injected O2, and the CO and CO2 capture units required for deep storage 9. This results in 300 MW of electricity for the Transmission Grid.
CONCLUSION
[0024] The result, a conservative one, shows that a 150 MW SMR used within the OLIVIA Cycle can generate 300 MW of electricity for the Grid. This must be compared to only 50 MW of electricity that the same 150 MW SMR would generate if used within a Rankine or Brayton cycle. These comparisons clearly demonstrate the power of using the SMR synergistically with coal, rather than letting the SMR work alone within an existing art steam or gas turbine cycle. Further, the OLIVIA cycle's zero carbon emissions must also be compared to significant emissions resulting from existing art steam or gas turbine plants burning fossil fuels.
[0025] While the present invention has been described in terms of particular details, in both summarized and detailed forms, it is not intended that these descriptions in any way limit its scope to any such details. It will be understood that many substitutions, changes and variations in the described details of the method and system illustrated herein, and of their operation, can be made by those skilled in the art without departing from the spirit of this invention.
