The disclosure broadly relates to renewable electricity, and more particularly, to a topping cycle that utilizes combustion energy electricity generation, such that the electricity output of the system exceeds the combined standalone outputs.
As world population continues to grow, more diversification in the use of natural resources is desired. In particular, a sustainable approach that encompasses greater use of solar, wind, and biomass resources is sought to face oncoming challenges of supplying a growing population with its increasing power needs. A problem with current implementations of solar and wind resources is that they are not readily available when most needed, i.e., they are not dispatchable. On the other hand, surplus solar and wind electricity tend to remain unused and methods to store this electricity via batteries, for example, are expensive. Biomass is a relatively inexpensive dispatchable source of energy. An approach of integrating surplus renewable energy with biomass is desired.
Cogeneration plants which serve to turn biomass or other feedstock to electricity and heat are well known. Cogeneration plants which use a combined cycle (CC), link a Brayton to a Rankine cycle to achieve higher efficiencies through the use of waste heat delivered from a gas turbine to power a steam turbine. An advantage of cogeneration plants using a combined cycle approach is that efficiencies of plants are doubled compared to the simpler steam boiler plants. Current CC plant efficiencies are around 40% for commercially operating power plants in the United States and Spain.
There is substantial capital cost associated with the turbines and generators used in these plants, however, and these plants need to be operated on a continuous load basis. Cogeneration plants using a single cycle, such as coal-based power plants (the most numerous plants in operation today), typically achieve electrical efficiencies around 10-25% through the use of subcritical steam cooled gas turbines. Natural gas efficiencies are somewhat higher, according to U.S. Energy Information Administration.
Efforts are being made to increase the renewable component in electricity production throughout the world, in particular by wider deployment of cogeneration plants that utilize biomass as co-fuel. An attractive feature of using biomass is the rendering of electricity production carbon neutral. It is desirable to transfer aspects of combined cycle to decentralized small scale power systems. In particular, efficient portable server units that avail themselves of the efficiencies of a combined cycle, utilize dispatchable biomass, and exploit surplus renewable electricity are desired.
Integrated gasification combined cycle (IGCC) plants utilize gasifiers for syngas production, and this syngas is combusted in a combined cycle operation. The basic elements of a coal-based IGCC power plant are as follows. Coal slurry along with compressed air is fed to a gasifier which produces syngas typically comprised of a mixture of H2, CO, CO2, H2O, CH4, N2 and small quantities of hydrocarbons and H2S. The hot syngas exiting the gasifier is cooled via a radiant cooler and directed to scrubbers and filters comprising the syngas cleanup process. Clean syngas is fed to a gas turbine along with compressed air, at which point electricity is generated when the syngas is combusted and electricity is generated via rotary motion of a set of turbines. Exhaust heat out of the turbine is directed to a heat recovery unit which then directs heat to a steam turbine which also produces electricity. Thus there are two heat conversion mechanisms, one for high grade heat (out of the gas turbine) and one for the low grade heat (out of the steam turbine). This combined cycle plant is called a topping cycle plant. When carbon dioxide is captured via sorbents and released to be sequestered in geologic formations the processed is called carbon capture and sequestration (CCS).
In the present disclosure a cogeneration plant serves as a partial source of energy to indirectly heat an exterior gasifier. Indirectly heated gasifiers are known. In a power system design by Battelle, Inc. as disclosed in U.S. Pat. No. 4,828,581, an entrained flow gasifier receives biomass as input and steam as the gasification medium, while a separate combustion chamber receives oxygen and char. The combusted char supplies energy to the first gasifier. Sand is used as the transfer medium between the gasifier and the char combustor. A tar cracker is used to eliminate tar resulting from the gasification. All the gasification energy comes from the input biomass and there is no non-thermal energy input to the char combustor or the gasifier.
Another gasifier indirect heating scheme is the separate chamber design as delineated by Cortus Energy in U.S. Pat. No. 8,617,268. In this gasification scheme gaseous flow and solid flow are separated by having three separate chambers, one for biomass drying, another for pyrolysis and yet another for char gasification. Pryrolysis gas and char are routed via separate streams to a gasifying chamber which also receives steam as an input. The pyrolysis step is performed at 400-500 C, while gasification occurs at 1100 C. The producer gas combustion and radiant heat from the pyrolysis step provide the energy for the gasification.
Embodiments of the present disclosure link idle power from renewable power plants, carbon from internal or external sources, and waste heat from a cogeneration plant to enable greater electricity production via gasification. The present disclosure represents an innovative method for storing energy from renewable sources and utilizing it in high efficiency power conversion systems. It further represents a novel pathway for a topping cycle cogeneration plant and a more efficient system integration of resources. Economical miniaturization of highly efficient combined cycle plants using natural gas or natural gas/biomass is realized. Implementation of gasification working at low pressures would save on capital costs of building additional large scale power plants. It is also represents a method for decarbonizing fossil-based methane.
The full nature of the advantages of the disclosure will become more evident from the following detailed description.
Certain embodiments of the present disclosure will hereinafter be described in detail, by way of example only, with reference to the accompanying drawings, in which:
In the following paragraphs, embodiments of the present disclosure will be described in detail by way of example with reference to the attached drawings. Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present disclosure. As used herein, the “present disclosure” refers to any one of the embodiments of the disclosure described herein, and any equivalents. Furthermore, reference to various feature(s) of the “present disclosure” throughout this document does not mean that all claimed embodiments or methods must include the referenced feature(s).
The possible inputs and outputs of the present disclosure are more fully shown in
This basic framework can be replicated a plurality of times, by using waste heat from one process to feed a subsequent process. This replicability is exemplified by
An alternate configuration of the present disclosure is presented in
The carbon-containing input 100 can be a material, gas, liquid or solid, or a mixture of materials, with a substantial fraction of carbon in its composition. This material may comprise part of a larger set of materials, some of which may have a small fraction or no fraction of carbon in its their composition. Carbon-containing input may comprise methane or methane-containing containing mixtures, such as natural gas, biogas, or landfill gas. The carbon-containing input may also comprise biomass, a term for the biodegradable fraction of agricultural products, residual or not, forestry products, industrial or municipal solid waste. Biomass generally refers to material originating from plant matter, in particular material containing cellulose, hemicellulose, lignins, lignocellulosic polymers, and extractives as composition. Forest products refers may refer to forest residue, wood pellets, wood shavings, bark, peat, waste wood, energy crops, virgin wood, recycled wood, sludge, sawdust, wood chips, as well as as black liquor and other products derived from pulp and paper operations. Biomass may also refer to herbaceous material such as miscanthus, rice husk, straw, and and sorghum as well as waste edible materials such as seeds and grains. Biomass may also refer to animal derived products such as manure. The term may also be used for a mixture of one or more of the above.
Industrial co-products may comprise biosolids, kitchen waste, medical waste, municipal solid waste, chemical waste, fabrics, plastic waste containing one of polyethylene, polypropylene, polyethylene terephthalate, polystyrene, polyvinyl chloride; tires and tire products, and fabrics.
The cogeneration plant 10 receiving carbon-containing input 100 serves to convert the input to electricity and useful heat. It comprises one or more heat engines and generators. The useful heat from the heat engine may be used in a variety of applications, some to produce electricity. Cogeneration plants include any topping cycle plants, and bottoming cycle plants. In particular, included are power plants supplying electricity and district heating, IGCC plants running on coal, biomass, or natural gas; CHP plants running gas turbines, steam turbines, rotary gas engines, reciprocating gas engines including internal and external combustion engines; plants running completely or partly on biomass such as wood pellets, plants using nuclear power, hybrid CHP plants running on solar power (ISCC, photovoltaic or concentrated) and natural gas, wind power and natural gas, hydrothermal power and coal; small scale CHP systems including microCHP system, trigeneration plants, and industrial cogeneration plants using boilers.
The extra process heat 120 may comprise 1-90% of the total chemical energy of input 100. In some embodiments, it may comprise 20-80% of the input energy, while in other embodiments it may comprise 30-70% of the input energy. Preferred embodiments comprise 20-50% of the input energy.
The optional carbon output 130 is a carbonaceous material that may arise from a pyrolysis or gasification process in a cogeneration plant. This carbonaceous product can be used in a subsequent gasifier 140 to effect various gasification reactions, such as gasification with steam, oxygen, carbon dioxide or hydrogen as follows:
C+H2O→CO+H2
C+CO2→2 CO
C+½ O2→CO
C+2H2→CH4
The carbon can be conveyed by various methods, such as transport in a moving conveyor, fine particle dispersal or pumped in slurry form. The external carbon source 160 can carbonaceous products such as charcoal, of renewable or fossil origin, biochar, activated carbon, or coal. Other carbon sources may derive from stranded natural gas, biogas, or landfill gas.
A notable feature of the present disclosure involves the utilization of both waste heat from the cogeneration plant and external high grade energy to power gasifier 140. By contrast, conventional gasifiers use just low grade energy for their operation. Gasifier reactions can be exothermic or endothermic, though most tend to be endothermic. Table 1 (below) lists common gasifier reactions along with enthalpies at various three different temperatures, and
In the presence of methane, the steam reforming reaction is possible, as shown by the following equation:
CH4+H2O→CO+3H2
A wide variety of gasifiers have been developed. Among the gasifiers suitable for the embodiments of the disclosure are the following: circulating fluidized bed or bubbling fluidized bed gasifiers, oxygen/steam/air blown gasifiers, fixed bed gasifiers, entrained flow gasifiers, and twin-bed gasifiers. The gasifier can be operated at atmospheric pressure or in pressurized mode.
While it may seem paradoxical to use electricity to generate electricity, a novel aspect of the disclosure involves time shifting the availability of idle electricity via the chemical energy stored in carbon. The source of the external energy may be any source of high grade heat, such as that available from electricity derived from solar and wind power plants. Solar power plants may utilize technology using photovoltaics, concentrated solar power using Fresnel collectors or parabolic mirrors, and non-concentrated solar-thermal systems. Suitable wind power plants include utility-style wind farms, small scale distributed wind plants, and off-shore wind plants. The extra energy may also be derived from a high temperature air combustion (HITAC) process where the waste energy is at sufficiently high temperature to be useful.
As mentioned above, carbon may be introduced from either the first gasifier or an external source. The calorific value (HHV) of char is approximately 30 MJ/kg, which represents 8.3 kWh per kg of char. In the case of concurrent steam injection into the gasifier, the external energy and the waste heat enable the gasification of this carbon and subsequent syngas production for electricity production, thus effecting a conversion from electricity to chemical energy and back to electricity.
Various embodiments for heating the second gasifier are shown in
Referring again to
The COEP, as defines herein, is a measure of the apparent amplification of the supplied external energy implemented via stored chemical energy in the supplied char and via use of process heat. By design in the present disclosure COEP is necessarily greater than 1. The apparent amplification (COEP>1) is a result of using electricity and waste heat from the combustion process. The overall thermal efficiency of the plant is still under 100%. The value of COEP is dictated by the ratio of supplied char to supplied external energy. In some embodiments COEP can vary from 1.01 to 10. Further embodiments have values COEP values from 1.5 to 5, and still further embodiments have COEP values from 2 to 4.
In a similar manner,
One skilled in the art will appreciate that the present disclosure can be practiced by other than the various embodiments and preferred embodiments, which are presented in this description for purposes of illustration and not of limitation, and the present disclosure is limited only by the claims that follow. It is noted that equivalents for the particular embodiments discussed in this description may practice the disclosure as well.
While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example only, and not of limitation. Likewise, the various diagrams may depict an example architectural or other configuration for the disclosure, which is done to aid in understanding the features and functionality that may be included in the disclosure. The disclosure is not restricted to the illustrated example architectures or configurations, but the desired features may be implemented using a variety of alternative architectures and configurations. Indeed, it will be apparent to one of skill in the art how alternative functional, logical or physical partitioning and configurations may be implemented to implement the desired features of the present disclosure. Also, a multitude of different constituent module names other than those depicted herein may be applied to the various partitions. Additionally, with regard to flow diagrams, operational descriptions and method claims, the order in which the steps are presented herein shall not mandate that various embodiments be implemented to perform the recited functionality in the same order unless the context dictates otherwise.
Although the disclosure is described above in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead may be applied, alone or in various combinations, to one or more of the other embodiments of the disclosure, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments.
Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open ended as opposed to limiting. As examples of the foregoing: the term “including” should be read as meaning “including, without limitation” or the like; the term “example” is used to provide exemplary instances of the item in discussion, not an exhaustive or limiting list thereof; the terms “a” or “an” should be read as meaning “at least one,” “one or more” or the like; and adjectives such as “conventional,” “traditional,” “normal,” “standard,” “known” and terms of similar meaning should not be construed as limiting the item described to a given time period or to an item available as of a given time, but instead should be read to encompass conventional, traditional, normal, or standard technologies that may be available or known now or at any time in the future. Likewise, where this document refers to technologies that would be apparent or known to one of ordinary skill in the art, such technologies encompass those apparent or known to the skilled artisan now or at any time in the future.
A group of items linked with the conjunction “and” should not be read as requiring that each and every one of those items be present in the grouping, but rather should be read as “and/or” unless expressly stated otherwise. Similarly, a group of items linked with the conjunction “or” should not be read as requiring mutual exclusivity among that group, but rather should also be read as “and/or” unless expressly stated otherwise. Furthermore, although items, elements or components of the disclosure may be described or claimed in the singular, the plural is contemplated to be within the scope thereof unless limitation to the singular is explicitly stated.
The presence of broadening words and phrases such as “one or more,” “at least,” “but not limited to” or other like phrases in some instances shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may be absent. The use of the term “module” does not imply that the components or functionality described or claimed as part of the module are all configured in a common package. Indeed, any or all of the various components of a module, whether control logic or other components, may be combined in a single package or separately maintained and may further be distributed across multiple locations.
Additionally, the various embodiments set forth herein are described in terms of exemplary block diagrams, flow charts and other illustrations. As will become apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives may be implemented without confinement to the illustrated examples. For example, block diagrams and their accompanying description should not be construed as mandating a particular architecture or configuration.
Number | Date | Country | |
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62108432 | Jan 2015 | US |