Patent Description:
The presently disclosed subject matter relates to systems and methods for generation of power, such as electricity, that operate at desirable efficiencies that are achieved through additive heating of at least part of a recycle CO<NUM> stream in a heat exchanger using a further heat source. Particularly, heat from the further source can be derived at least in part from compression of at least a portion of the recycle COz stream.

Conventional means of power production from combustion of a fuel typically lack the ability to simultaneously achieve high efficiency power generation and carbon capture (e.g., for sequestration or other use). One publication in the field of high efficiency power generation with carbon capture, <CIT>, provides for desirable efficiencies in closed cycle combustion systems using CO<NUM> as the working fluid. Such systems in particular benefit from the recognized usefulness of heating a recycle CO<NUM> stream in a recuperative heat exchanger using heat from the hot turbine exhaust as well as adding further heat from a source other than the turbine exhaust. Despite such advances, there is yet a growing need in the art for improved systems and methods for power generation that provide increased efficiency with capture of COz and other fuel and combustion derived impurities.

The present disclosure provides systems and methods of power production with improved efficiency. The systems and methods can utilize CO<NUM> as a working fluid and can be configured for capture of COz and other fuel and combustion derived impurities. The present improvements have been identified in relation to the introduction of low temperature level heating to a recycle CO<NUM> stream in an elevated pressure, oxy-fuel combustion system and method that also utilizes recuperative heating of the recycle CO<NUM> stream with heat from the hot turbine exhaust. The low temperature level heating can be described herein in terms of being "additive heating. " As such, it is understood that the additive heating is low temperature level heat from a source other than the hot turbine exhaust. In other words, the additive heating is not heat that is recuperated from the hot turbine exhaust. The present disclosure in particular identifies means for obtaining and transferring the additive heating in a closed cycle or partially closed cycle oxy-fuel combustion system and method that provides a power production output that exceeds the heating capacity of the heat from the fuel alone and thus provides an advantageous increase in efficiency.

The present disclosure relates to systems and methods for generation of power, such as electricity, that operate at desirable efficiencies that are achieved through the combustion of a fuel (e.g., a carbonaceous or carbonaceous fuel) in oxygen at elevated pressure in the presence of a recycle CO<NUM> stream followed by expansion of the product gas through a power producing turbine and cooling of the turbine exhaust in a recuperative heat exchanger, which heats the previously compressed recycle CO<NUM> stream. Improved efficiency of power generation can be obtained by additive heating of at least part of the recycle CO<NUM> stream in a heat exchanger using additive heating, which can be, for example, heat derived at least in part from compression of at least a portion of the recycle CO<NUM> stream.

In various embodiments, power production can be achieved utilizing a closed cycle or partially closed cycle system in which CO<NUM> is utilized as the working fluid. In such systems, a fossil fuel (e.g., natural gas) or a fuel derived from a fossil fuel (e.g., syngas derived from coal or other solid carbonaceous fuel) is completely combusted in a combustor using substantially pure oxygen as the oxidant to give an oxidized stream of predominantly CO<NUM>, H<NUM>O, excess Oz, and a quantity of impurities derived from oxidized components in the fuel or oxidant, such as SOz, NOx, Hg, and HCl. Solid fossil fuels, such as coal, lignite, or petroleum coke, that contain non-combustible ash may be converted to a gaseous fuel by partial oxidation in a single stage or multi-stage system. Such system, for example, may comprise a partial oxidation reactor. Alternatively, for example, such system may comprise a partial oxidation reactor and an ash and volatile inorganic component removal system. Such systems further comprise combustion of the fuel gas with oxygen in the combustor of the power production system. A preheated recycle CO<NUM> stream is mixed in the combustor with the combustion products derived from combustion of the fuel gas. Any combustor adapted for operation under conditions otherwise described herein may be used, and the recycle CO<NUM> stream may be introduced to the combustor by any means to be further heated by the combustion and, if desired, to quench and thereby control the temperature of the exit stream. In some embodiments, one or both of a POX reactor and the combustor may utilize, for purposes of example only, a transpiration cooled wall surrounding the reaction or combustion space, and the preheated recycle CO<NUM> stream may pass through the wall to both cool the wall and to quench and thereby control the temperature of the exit stream. The transpiration flow promotes good mixing between the recycle CO<NUM> and the hot combusted fuel gas streams. Other types of combustors, however, may also be used, and the present disclosure is not limited to the use of transpiration cooled combustors. Although certain fuel types are exemplified above, it is understood that other fuels (e.g., hydrogen) may be utilized in the combustor. Likewise, the advantages flowing from the use of additive heat may be applied to systems utilizing non-combustion heating in part or in total. For example, use of solar systems such as described in <CIT> is also encompassed by the present disclosure.

The combined combustion products and preheated recycle CO<NUM> leaving the combustor are at the temperature required for the inlet to a power-producing turbine. The CO<NUM> power cycle can use a pressure ratio across the turbine from <NUM> to <NUM> in some embodiments, although greater pressure ratios (e.g. at least <NUM>) may be used in other embodiments, such as when utilizing a plurality of expansion turbines. A turbine inlet pressure of about <NUM> bar (10MPa) to about <NUM> bar (<NUM> MPa) can be used in some embodiments. The oxygen supplied to the combustor can be either substantially pure O<NUM> or O<NUM> diluted with COz. In some embodiments, mixing of the Oz and CO<NUM> can be useful to control the adiabatic flame temperature of the combustion reaction. As a non-limiting example, the molar concentration of Oz in the combined O<NUM>/CO<NUM> stream can be about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>%. The hot turbine exhaust can be cooled in an economizing heat exchanger, which in turn preheats the high pressure CO<NUM> recycle stream.

The efficient operation of the system is critically dependent on the optimization of the heat exchange. To achieve a high efficiency, a large quantity of additive heat can be added into the high pressure recycle stream at the cold end of the heat exchanger, such as at a temperature level from about <NUM> to about <NUM>. This low temperature level heat may be derived in some embodiments from the air compressors of a cryogenic oxygen plant, which compressors may be operated wholly or in part with their pressure ranges in a high-pressure ratio adiabatic mode so that the compressed air is raised in temperature at the stage discharge to a point in the range of about <NUM> to about <NUM> and so that heat transfer from the compressed air stream to the pressurized recycle CO<NUM> process stream can be easily accomplished. For example, a side stream flow taken from the high pressure CO<NUM> recycle flow in the economizer heat exchanger can be heated against cooling compressed air to a required temperature of about <NUM> to about <NUM>. Systems and methods for such oxyfuel combustion, low level heat production, and low level heat transfer are described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

The present disclosure provides further means for introducing heat into a recycle CO<NUM> high pressure stream at a temperature of about <NUM> to about <NUM> and thus increase the effectiveness of an economizer heat exchanger and increase the overall efficiency of the power production system and method incorporating the present heat transfer means. In particular, the present disclosure provides for the use of a portion of the heat of compression from a recycle CO<NUM> compressor as the additive heating necessary to increase the overall efficiency of a power production system and method.

Previous proposals have been made to optimize the performance of a power production cycle using high pressure CO<NUM> as the working fluid. For example, <NPL> presentation at the supercritical CO<NUM> power cycle workshop in Boulder, Colorado) describes Brayton cycles for power generation using recuperator heat exchanger with CO<NUM> as the working fluid. The paper defines the efficiencies of two cycles in terms of operating parameters and shows the conditions under which the second cycle gives a higher efficiency than the first, simple cycle.

The first, simple cycle from Bryant et al. is shown in <FIG>. Therein, hot CO<NUM> in line <NUM> that has been compressed in a near adiabatic, non-intercooled compressor <NUM> is further heated in a recuperator heat exchanger <NUM>. The hot CO<NUM> then passes through line <NUM> to the heater <NUM> where it is heated either directly by combusting a fuel <NUM> with oxygen <NUM>, or by some means of external heating. The further heated CO<NUM> then passes through line <NUM> into a power producing turbine <NUM> where it is expanded to a lower pressure producing shaft work (illustrated by arrow <NUM>). The turbine exhaust stream <NUM> passes to the recuperator heat exchanger <NUM> where it cools releasing heat to the high pressure recycle stream. The turbine exhaust is then cooled in a pre-cooler <NUM> where heat is rejected to a cooling stream <NUM> that exits via line <NUM> before finally re-entering the compressor <NUM> in line <NUM>.

The second cycle from Bryant is shown in <FIG>, which is identical to the cycle shown in <FIG> apart from the addition of a second compression stage <NUM> in which part of the low pressure turbine exhaust stream <NUM> leaving the low pressure return circuit at the exit from the recuperator heat exchanger 4a before the pre-cooler <NUM> is compressed in its hot condition in compressor <NUM> leaving through line <NUM>. This stream enters the recuperator heat exchanger 4b after mixing with the main high pressure recycle stream leaving 4a at its corresponding temperature and is heated in heat exchanger section 4b against hot turbine exhaust stream <NUM>. The effect of the additional compression is to inject a large amount of heat into the recuperator heat exchanger from the second compressor which takes as its inlet flow a CO<NUM> stream at an elevated temperature which is greater than the inlet temperature of the main CO<NUM> compressor.

The teaching of Bryant et al. reveals a disadvantage in that the heat input by-passes the first stage of the recuperator heat exchanger 4a. The much larger specific heat of the high pressure COz stream that is being heated in heat exchanger 4a compared to the low pressure turbine exhaust stream cooling in heat exchanger 4a means that the heat transfer in heat exchanger 4a into the high pressure stream must be maximized to achieve a close temperature approach. This is not achieved since the heated compressed CO<NUM> stream bypasses heat exchanger 4a. What is required for the maximum efficiency is to arrange a hot gas compression system in which the compressed CO<NUM> cools down in the heat exchanger and increases the available heat transfer to the high pressure CO<NUM> stream. The present disclosure relates in part to means for overcoming this disadvantage.

Although the cycles from Bryant et al. illustrated in <FIG> and <FIG> represent the known prior art for hot CO<NUM> compression, they are only suitable for use in simple Brayton cycle arrangements that use a main COz compressor without intercoolers giving a high discharge temperature. This in turn causes the cooling turbine discharge flow leaving the recuperator heat exchanger 4a to also be at a high temperature so the heat rejected in the pre-cooler heat exchanger is also high. It is therefore apparent that optimum efficiencies will only be achieved at low pressure ratios in this hot compression cycle which are shown to be in the range of <NUM> to <NUM> with optimum main compressor inlet pressures near the critical pressure of COz. Higher pressure ratios lead to excessive heat losses in the system. The Bryant et al. cycles shown in <FIG> and <FIG> also fail to account for system details such as the presence of liquid water separation in the compressor inlet lines <NUM> following cooling in the heat exchanger <NUM> against ambient cooling means.

The Bryant et al. cycle in <FIG> has several further limitations. For example, the Bryant et al. cycle efficiency significantly decreases as the pressure ratio is increased since the main and recompression compressors are essentially adiabatic in operation with no intercoolers between stages. The studies reported by Bryant et al. show that the optimum pressure ratio for a turbine inlet temperature of <NUM> is <NUM> at a turbine inlet pressure of <NUM> bar and <NUM> at a turbine inlet pressure of <NUM> bar. Low pressure ratios require very high CO<NUM> flow-rates in the system for a given power output leading to high capital costs. On the contrary, the present disclosure provides cycles with high pressure ratios and high turbine inlet pressures resulting in high efficiency and low capital cost.

Systems and methods useful according to the present disclosure can utilize pressure ratios of about <NUM> or greater, such as about <NUM> to about <NUM>. In some embodiments, pressure ratios preferably can be in the range of about <NUM> to about <NUM>. The present systems and methods also can utilize intercooled main CO<NUM> recycle compression systems. The high pressure ratio favors a turbine inlet pressure above the CO<NUM> critical pressure of <NUM> MPa and a turbine discharge pressure below this pressure. These higher pressure ratios give high efficiencies of <NUM>% to <NUM>% for natural gas fueled systems with significantly lower circulation rates of CO<NUM> per kW of net power output. Systems and methods useful according to the present disclosure also preferably utilize a very considerable input of additive heat at a temperature level of, for example, greater than <NUM>, and particularly in the range of about <NUM> to about <NUM> or about <NUM> to about <NUM>. The presently disclosed systems and methods are particularly beneficial in providing for utilization of a portion of the heat of compression from the main recycle CO<NUM> compressor as this additive heating.

The present disclosure provides a power generating system according to claim <NUM>.

The present disclosure further relates to a method of generating power according to claim <NUM>.

The present subject matter will now be described more fully hereinafter with reference to exemplary embodiments thereof. These exemplary embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art. Indeed, the subject matter can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

The present disclosure relates to systems and methods that provide power generation using predominantly CO<NUM> as a working fluid. In particular, the process uses a high pressure/low pressure ratio turbine that expands a mixture of a high pressure recycle CO<NUM> stream and combustion products arising from combustion of the fuel. Any fossil fuel, particularly carbonaceous fuels, may be used. Non-limiting examples include natural gas, compressed gases, fuel gases (e.g., comprising one or more of H<NUM>, CO, CH<NUM>, H<NUM>S, and NH<NUM>) and like combustible gases. Solid fuels - e.g., coal, lignite, petroleum coke, bitumen, biomass, and the like, or viscous liquid fuels may be used as well with incorporation of necessary system elements. For example, a partial oxidation combustor can be used to convert the solid or viscous liquid fuel to a fuel gas that is substantially free of solid particles. All fuel and combustion derived impurities in an oxidized state, such as sulfur compounds, NO, NOz, COz, HzO, Hg, and the like can be separated from the power cycle for disposal with substantially or completely no emissions to the atmosphere. As noted previously, other fuels likewise may be utilized. Pure oxygen can be used as the oxidant in the combustion process. In some embodiments, combustion temperature may be regulated by diluting the oxygen with CO<NUM> in ratios as otherwise noted herein.

The hot turbine exhaust is used to partially preheat the high pressure recycle CO<NUM> stream. In combination with this heating, the recycle CO<NUM> stream is further heated using additive heating that can be derived from the compression energy of a CO<NUM> compressor. The operating conditions for the CO<NUM> compressor can vary as further described herein. For example, in some embodiments, it can be useful to utilize a CO<NUM> compressor inlet temperature that is higher than normal approach to ambient cooling means. The minimum inlet temperature of the stream entering the COz compressor, for example, can be approximately the dew point of water at the operating conditions. In some embodiments, the CO<NUM> compressor can have an inlet temperature of about <NUM> to about <NUM>. At least one other heating means providing heat at a temperature level below about <NUM> is be used in addition to the heating available from the CO<NUM> compression. Such means can include heat transferred from the air compressors of a cryogenic air separation plant operating partially or completely in the adiabatic mode without intercooling. When such heat is utilized, the air compressors preferably can be operated with pressure ratios above <NUM> in the adiabatic stages.

It has been discovered according to the present disclosure that power production efficiency can be improved through provision of additive heating as defined herein, such additive heating particularly being provided at a temperature level below about <NUM> (e.g., in the range of about <NUM> to about <NUM>). The provision of the additive heating can overcome the large difference in the specific heat of CO<NUM> at a typical high pressure turbine inlet of about <NUM> bar (<NUM> MPa) and the specific heat of CO<NUM> at a typical low pressure turbine exhaust pressure of about <NUM> bar (<NUM> MPa). This difference is evident in the table provided below.

A power production method according to the present disclosure particularly comprises a series of steps that can provide for improved efficiency. The method comprises passing a compressed, heated recycle CO<NUM> stream into a combustor. The compressed, heated recycle CO<NUM> stream can be formed as further described below. In the combustor, a fuel is combusted with the oxidant (e.g., oxygen of at least <NUM>% or at least <NUM>% purity, optionally diluted with COz) in the presence of the recycle CO<NUM> stream to produce a CO<NUM> containing stream. The CO<NUM> containing stream from the combustor can have a temperature of about <NUM> or greater (e.g., about <NUM> to about <NUM>,<NUM> or about <NUM> to about <NUM>,<NUM>) and a pressure of about <NUM> bar (<NUM> MPa) or greater (e.g., about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa)). The CO<NUM> containing stream is passed through a turbine to expand the CO<NUM> containing stream, generate power, and form a turbine exhaust stream comprising COz. The CO<NUM> containing stream can be expanded across the turbine at a pressure ratio of less than <NUM> or less than <NUM> (e.g., about <NUM> to about <NUM>). In alternate embodiments, high pressure ratios as noted herein may be used, such as in the case of utilizing a plurality of turbines, as described in <CIT>.

The turbine exhaust stream can be processed to remove combustion products and any net CO<NUM> produced by combustion of the fuel. To this end, the turbine exhaust stream is cooled by passage through a heat exchanger. Any heat exchanger suitable for use under the temperature and pressure conditions described herein can be utilized. In some embodiments, the heat exchanger can comprise a series of at least two, at least three, or even more economizer heat exchangers. A single heat exchanger with at least two sections, at least three sections (or even more sections) can be used. For example, the heat exchanger may be described has having at least three heat exchange sections operating across different temperature ranges. Withdrawn heat from the turbine exhaust stream is utilized for heating the recycle CO<NUM> stream as described below.

The turbine exhaust stream is divided into two or more portions. The first portion can comprise <NUM>% or greater, <NUM>% or greater, or <NUM>% or greater (but less than <NUM>%) of the total mass flow of the turbine exhaust stream. The first turbine exhaust portion is cooled preferably at a temperature that is less than the water dew point after leaving the heat exchanger. The first turbine exhaust portion can be passed through a separator to remove water and can be further treated to remove other combustion products or impurities. The resulting stream can be described as a main recycle CO<NUM> stream, and this stream is compressed such as in a multi-stage compressor with intercooling between the stages. Preferably, the main recycle CO<NUM> stream is compressed to a pressure of about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa). In some embodiments, the main recycle CO<NUM> stream is compressed to a pressure of about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa) or about <NUM> bar (<NUM> MPa) to about <NUM> bat (<NUM> MPa).

The second portion of the turbine exhaust stream is compressed to form a heated, compressed second turbine exhaust portion. The second turbine exhaust portion can comprise the balance of the turbine exhaust not present in the first portion (e.g., <NUM>% or less, <NUM>% or less, or <NUM>% or less (but greater than <NUM>%) of the total mass flow of the turbine exhaust stream).

Preferably, the second turbine exhaust portion can be withdrawn from the turbine exhaust between the second and third heat exchange sections (e.g., the second and third heat exchangers in the series moving from hot to cold - in other words, the heat exchangers working between the lowest temperature and an intermediate temperature). The second turbine exhaust portion is preferably compressed so as to achieve a temperature in the range of about <NUM> to about <NUM> and a pressure of about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa). In some embodiments, the pressure can be about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa) or about <NUM> bat (<NUM> MPa) to about <NUM> bar (<NUM> MPa). The second turbine exhaust portion is re-introduced to the heat exchanger, preferably passing from the hot end of the intermediate temperature heat exchanger to the cold end of the low temperature heat exchanger. The cooled second turbine exhaust portion can be at a temperature that is below the water dew point, and the cooled stream can be passed through one or more separators to remove water and any other impurities. The remaining stream is a secondary recycle CO<NUM> stream, and it is combined with the main recycle CO<NUM> stream. Such combining can be at a variety of points. For example, the main recycle CO<NUM> stream can be added to the cooled second portion of the turbine exhaust after passage through the low temperature heat exchanger and before passage through the separator. Alternatively, the main recycle CO<NUM> stream and the secondary recycle CO<NUM> stream can be combined after water separation or at another point of the cycle. Net CO<NUM> produced from combustion can be withdrawn at this point, such as for use in enhanced oil recovery, for sequestration, or the like.

In some embodiments, the second turbine exhaust portion can be compressed using multi-stage compression wherein there is no inter-cooling between stages followed by inter-cooling between later stages. Compressed and heated gas of the second turbine exhaust portion exiting the non-cooled stages can be introduced to the heat exchanger as otherwise described above, and the so-cooled stream can be subjected to the inter-cooled compression before combining with the first turbine exhaust portion. The number of non-cooled stages (x) and inter-cooled stages (y) can independently be <NUM> or more, <NUM> or more, or <NUM> or more (e.g., <NUM> to <NUM> or <NUM> to <NUM>).

The total recycle CO<NUM> stream (formed of the main recycle CO<NUM> stream and the secondary recycle CO<NUM> stream) is pumped to a pressure suitable for passage into the combustor. Preferably, the total recycle CO<NUM> stream is pumped to a pressure of at <NUM> bar (<NUM> MPa) or greater or about <NUM> bar (<NUM> MPa) or greater, such as about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa). The compressed recycle CO<NUM> stream is then passed back through the heat exchangers to be heated. The compressed recycle CO<NUM> stream is heated using the heat withdrawn from the turbine exhaust stream (which can be characterized as the heat of combustion that remains in the turbine exhaust stream). The heat in the turbine exhaust stream, however, is insufficient to achieve a close temperature approach between the turbine exhaust stream and the heated, compressed recycle CO<NUM> stream at the hot end of the heat exchanger. According to the present disclosure, the heat from the compressed, second turbine exhaust portion is used as additive heating to reduce the temperature differential between the turbine exhaust stream and the heated, compressed recycle CO<NUM> stream leaving the heat exchanger and entering the combustor. The additive heating can be characterized as the heat of recompression and is separate from the heat of combustion that is present in the turbine exhaust. The use of the additive heating can be beneficial to reduce temperature differential between the turbine exhaust stream and the heated, compressed recycle CO<NUM> stream leaving the heat exchanger and entering the combustor to about <NUM> or less, about <NUM> or less, or about <NUM> or less, such as about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

At least one additive heating is provided by other means in combination with the heat of recompression. For example, heated CO<NUM> from an external source can be utilized. Such external source can be, for example, CO<NUM> withdrawn from a geological source, CO<NUM> taken from a pipeline, or the like. In such embodiments, splitting of the turbine exhaust stream can be unnecessary, such embodiments not forming part of the claimed invention, and the heated CO<NUM> can be input to the system in the same manner as the heat of recompression described above. The additional CO<NUM> can be withdrawn from the system with the net COz product and can be returned to the heat source. In such manner, a recycled CO<NUM> from an external source completely outside of the power production system can be utilized as additive heating. Alternatively, part or all of the additive heating can be from a gas turbine exhaust or from a condensing stream.

An exemplary embodiment of a system according to the present disclosure is shown in <FIG>. The embodiment is described in relation to an exemplary embodiment of a combustion method utilizing defined parameters. Specific temperatures and pressures thus can vary based upon the specific operation conditions.

In the embodiment of <FIG>, a turbine exhaust stream <NUM> at <NUM> and <NUM> bar (<NUM> MPa) passes through three economizer heat exchangers in series <NUM>, <NUM>, and <NUM> leaving as stream <NUM> at <NUM> and <NUM> bar (<NUM> MPa). Heat exchanger <NUM> may be characterized as a high temperature heat exchanger, heat exchanger <NUM> may be characterized as an intermediate temperature heat exchanger, and heat exchanger <NUM> may be characterized as a low temperature heat exchanger. It is understood that the terms "high temperature," "intermediate temperature," and "low temperature," are intended to only describe the operating temperature ranges of the three heat exchangers relative to one another. The stream <NUM> is cooled in a water cooled heat exchanger <NUM> to <NUM>, and a condensed water stream <NUM> is separated in the phase separator vessel <NUM>. An overhead CO<NUM> gas stream <NUM> leaves the phase separator vessel <NUM> and enters a two stage centrifugal CO<NUM> recycle compressor <NUM> (stage <NUM>) and <NUM> (stage <NUM>), wherein a discharge stream <NUM> from the first stage compressor <NUM> is cooled in an intercooler <NUM> to <NUM>, exits as stream <NUM>, and is then compressed in the second stage compressor <NUM> to form stream <NUM> at <NUM> bar (<NUM> MPa). This main recycle compressor discharge stream <NUM> joins with stream <NUM>, and the combined stream <NUM> is cooled in a water cooled heat exchanger <NUM> to a temperature of <NUM>. In other embodiments, this temperature can be in the range of <NUM> to about <NUM>. Condensed water <NUM> is separated in a phase separator <NUM> producing the total recycle CO<NUM> stream <NUM>, which is in the supercritical state and has a high density of <NUM>/m<NUM>. A net product CO<NUM> stream <NUM>, equivalent to the carbon in the fuel gas converted to CO<NUM> in the combustor, is removed from the system (after cooling, as illustrated, or before cooling) for sequestration, use in enhanced oil recovery, or the like.

The total recycle CO<NUM> stream <NUM> is cooled in heat exchanger <NUM> to a temperature of <NUM> then enters a multi-stage centrifugal pump <NUM> with a discharge pressure of <NUM> bar (<NUM> MPa) to from a high pressure CO<NUM> recycle stream <NUM>, which is heated in the three economizer heat exchangers in series <NUM>, <NUM> and <NUM> leaving as stream <NUM> at a temperature of <NUM> and <NUM> bar (<NUM> MPa). The stream <NUM> is heated to <NUM> in combustor <NUM> by the direct combustion of a natural gas stream <NUM> with a <NUM>% Oz stream <NUM>, both at <NUM> bar (<NUM> MPa). In the exemplified embodiment, modeling was done with pure CH<NUM> as the fuel gas. The mixed stream of recycle CO<NUM> and combustion products <NUM> enters a power turbine <NUM> with a discharge pressure of <NUM> bar (<NUM> MPa) and exits as turbine exhaust stream <NUM>.

As seen in the table above, the difference in the specific heat of CO<NUM> at <NUM> bar (<NUM> MPa) and <NUM> bar (<NUM> MPa) increases as the temperature drops from <NUM> (<NUM>). In light of this difference, additive heating is required to achieve a very close temperature approach between the turbine exhaust stream <NUM> and the recycle CO<NUM> stream <NUM>, and such additive heating can be supplied, for example, in the "low temperature" economizer heat exchanger <NUM> and/or the "intermediate temperature" economizer heat exchanger <NUM>. According to the present disclosure, the additive heating can be provided by utilizing the adiabatic heat of compression of part of the recycle CO<NUM> stream which, in the exemplary embodiment, is compressed to a pressure of about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa).

Returning to the exemplary embodiment of <FIG>, a portion of the cooling turbine exhaust stream <NUM> between the two economizer heat exchanger sections <NUM> and <NUM> at a temperature of <NUM> is withdrawn and compressed in a single stage or multi-stage adiabatic compressor <NUM> producing stream <NUM> at <NUM> and <NUM> bar (<NUM> MPa). The compressed and heated stream <NUM> re-enters the hot end of economizer heat exchanger <NUM>, and the stream is passed through heat exchanger <NUM> and heat exchanger <NUM> where it cools and leaves as stream <NUM> at <NUM>. The entire heat of compression in compressor <NUM> supplied by work stream <NUM> is thusly transferred to the high pressure recycle CO<NUM> stream, and this heat input is equivalent to heat of combustion delivered in the combustor <NUM> since it reduces the hot end temperature difference. The flow-rate of stream <NUM> is maximized to achieve a significantly small temperature difference between streams <NUM> and <NUM> at the inlet to the high temperature economizer heat exchanger <NUM>. This temperature difference between streams <NUM> and <NUM> preferably is about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, particularly about <NUM> to about <NUM>, or about <NUM> to about <NUM>. As discussed above, stream <NUM> joins with the main recycle compressor discharge stream <NUM> for cooling in heat exchanger <NUM> to <NUM>. The additive heating provide by CO<NUM> compression as described above provides for increased efficiency in the power production system.

Note that other sources of low temperature level heating (e.g., gas turbine exhaust or condensing stream) can be utilized as additive heating. The exemplary embodiment of <FIG> includes the cryogenic air separation plant <NUM> main air flow 42a which has been adiabatically compressed to <NUM> bar (<NUM> MPa) and <NUM> entering the hot end of economizer heat exchanger <NUM> as stream <NUM> and leaving heat exchanger <NUM> as stream <NUM> at <NUM>. In some embodiments, stream <NUM> may arise from stream 42b, which is illustrated as heat derived from a gas turbine <NUM>. Although not illustrated in <FIG>, in some embodiments, the Oz stream can be supplied from the air separation plant at <NUM> bar (<NUM> MPa) and ambient temperature and can be mixed with CO<NUM> from stream <NUM> to give <NUM> mol% Oz that can be compressed to <NUM> bar (<NUM> MPa) before being heated to <NUM> in the economizer heat exchangers <NUM>, <NUM> and <NUM>. In practice, this CO<NUM>+O<NUM> compressor can also feature a hot gas compressor section as has been shown for the CO<NUM> recycle compressor. In <FIG>, cooling water inlet streams are represented as streams <NUM>, <NUM>, <NUM>, and <NUM>, while the respective outlet streams are represented as streams <NUM>, <NUM>, <NUM>, and <NUM>. The compressor power inputs are illustrated in <FIG> as elements <NUM> and <NUM>, and such power inputs may be electric or may be turbine driven. The COz pump electric power input is illustrated as element <NUM>. The turbine shaft power output is illustrated as element <NUM> from the generator <NUM>.

The exemplary embodiment described was evaluated with ASPEN modeling software using actual machine efficiencies, heat exchanger temperature differences, and system pressure drops giving a net efficiency of <NUM>% (LHV basis). The calculation was based on a thermal input of <NUM> MW to the combustor <NUM>.

Although the disclosed systems and methods may be particularly applicable to combustion systems and methods for power production, a broader application to efficient heating of a gas stream is also encompassed, such embodiments not forming part of the claimed invention. As such, in some embodiments, the present disclosure can relate to a method for heating a gas stream, and particularly for heating a recirculating gas stream. The recirculating gas stream may be any gas stream that is continuously cycle through stages of heating and cooling, optionally including stages of compression and expansion.

A gas stream G that may be subject to heating according to the present disclosure may be any gas; however, it can be particularly advantageous for the gas stream G to comprise CO<NUM>, such as being at least about <NUM>%, at least about <NUM>%, at least about <NUM>%, at least about <NUM>%, or at least about <NUM>% by mass COz. A recirculating gas stream G particularly may be at increased temperature T<NUM> (e.g., about <NUM> to about <NUM>) and a pressure P<NUM> that enables forming a desired amount of heat of compression - e.g., a pressure of less than about <NUM> bar (<NUM> MPa). The gas stream G at pressure P<NUM> and temperature T<NUM> can be cooled, such as by passage through a recuperative heat exchanger. Preferably, cooling is such that the gas stream G is cooled to a temperature T<NUM> that is less than T<NUM>. In some embodiments, cooling can be carried out using a series of multiple heat exchangers (e.g., <NUM>, <NUM>, or more heat exchangers) or using a heat exchanger that includes a plurality of heat exchange sections or using a combination thereof. The individual heat exchangers (or heat exchange sections) can exchange heat at different temperature ranges, which ranges may overlap. Use of multiple heat exchangers and/or heat exchange sections enables streams to be added or withdrawn at different temperature ranges.

The gas stream G can be separated into a first fraction G<NUM> and a second fraction G<NUM>. Such separation can occur after the gas stream G has been cooled to the temperature T<NUM> or to an intermediate temperature Tint that is between T<NUM> and T<NUM>. The temperature T<NUM>, for example, can be the temperature at the cold end of the recuperative heat exchanger (or the heat exchanger or heat exchange section working over the lowest temperature range), and the temperature Tint, for example, can be a temperature at the cold end of a second heat exchanger (or second heat exchange section) in a series of three or more heat exchangers (or heat exchange sections). Preferably, the second gas fraction G<NUM> can be withdrawn at an intermediate temperature prior to further cooling of the first gas fraction G<NUM>. After the gas stream fraction G<NUM> has been cooled, it can then be compressed to a greater pressure P<NUM> that preferably can be greater than P<NUM>. Such compression, for example, can be carried out with a multi-stage compressor that is intercooled. The pressure P<NUM> can be, for example, about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa), about <NUM> bar (<NUM> MPa) to about <NUM> bar (<NUM> MPa) or about <NUM> bar (<NUM> MPa) to about <NUM> bat (<NUM> MPa).

The withdrawn gas stream fraction G<NUM> can be separately compressed to a pressure P<NUM> that also preferably is greater than P<NUM>. The pressure P<NUM> can be in the same range of pressure P<NUM>; however, P<NUM> and P<NUM> do not necessarily need to be identical. In some embodiments, the gas stream fraction G<NUM> can be compressed using adiabatic compression with no intercooling so as to heat the gas stream fraction G<NUM> to a temperature T<NUM> that is greater than T<NUM>. In embodiments wherein the gas stream fraction G<NUM> can be withdrawn at the intermediate temperature Tint, T<NUM> preferably is greater than Tint. The heat from the compressed gas stream fraction G<NUM> can be withdrawn and used as additive heating to the recirculating gas stream as further described below.

After the compression heat has been withdrawn from gas stream fraction G<NUM>, the gas stream fraction G<NUM> and the gas stream fraction G<NUM> can be combined to form a combined recirculating gas stream Gc. The recirculating gas stream Gc will have a pressure that is substantially similar to the pressure P<NUM> and/or P<NUM> and can be pumped to a greater pressure P<NUM> that is greater than P<NUM> and greater than P<NUM>. Such pumping is desirable is the recirculating gas stream Gc is being utilized in a high pressure application. In some embodiments, however, the pressure P<NUM> and/or P<NUM> may be suitable and no further compression may be required.

The recirculating gas stream Gc (optionally at the pressure P<NUM>) can be passed to the recuperative heat exchanger such that the gas stream Gc is heated by the cooling gas stream G. The heat withdrawn from the compressed gas stream fraction G<NUM> can be added to the recirculating gas stream Gc. Such additive heating can be carried out after pumping to pressure P<NUM>. In some embodiments, the additive heating can be carried out in the recuperative heat exchanger. For example, if a single recuperative heat exchanger is used, the heat of compressed gas stream fraction G<NUM> can be input to the heat exchanger at a suitable point to provide the additive heating to the recirculating gas stream Gc in the desired temperature range. In embodiments wherein a plurality of heat exchanger (or heat exchange sections) are used, the heat of compressed gas stream fraction G<NUM> can be added to one or more of the lower temperature heat exchangers (or heat exchange sections). For example, during compression, gas stream fraction G<NUM> can be heated to a temperature in the range of about <NUM> to about <NUM>, and the heat from the compressed gas stream fraction G<NUM> can be added to one or more heat exchangers (or heat exchange sections) working in this temperature range. In <FIG>, for example, compressed gas stream fraction G<NUM> would equate to stream <NUM>, which is passed through heat exchangers <NUM> and <NUM>, which are working at a lower temperature range than heat exchanger <NUM>. Generally, a series of heat exchangers such as illustrated in <FIG>, comprises three heat exchangers that each transfer in separate temperature ranges (which ranges may overlap). In the example of <FIG>, heat exchanger <NUM> can be characterized as operating in a temperature range R<NUM>, heat exchanger <NUM> can be characterized as operating in a temperature range R<NUM>, and heat exchanger <NUM> can be characterized as operating in a temperature range R<NUM>. As illustrated, since heat exchanger <NUM> is at the hot end of the series and heat exchanger <NUM> is at the cold end of the series, the temperature relationship of the series of heat exchangers would be R<NUM>>R<NUM>>R<NUM>.

The use of the additive heating provided by the compression heat in compressed gas stream fraction G<NUM> can be beneficial to bring the temperature of the combined recirculating gas stream Gc significantly close to the temperature of gas stream G prior to cooling. For example, the recirculating gas stream Gc after passing through the recuperative heat exchanger and receiving the heat from the compressed gas fraction G<NUM> can have a temperature T<NUM> that is within <NUM> of T<NUM>. Typically, the temperature T<NUM> of recirculating gas stream Gc after passing through the recuperative heat exchanger will remain below T<NUM>. In such embodiments, recirculating gas stream Gc after passing through the recuperative heat exchanger and receiving the heat from the compressed gas fraction G<NUM> can have a temperature T<NUM> that is less than T<NUM> by no more than <NUM>.

The approach of T4 to T1 can be further improved through addition of heat from one or more additional sources. Such additional heat source can comprise any device or combination of devices configured to impart heating to a stream that is sufficient to heat a gas stream as described herein so that the gas stream achieves the desired quality and quantity of heat. As non-limiting examples, the additional heat source can be one or more of a combustion heat source, a solar heat source, a nuclear heat source, a geothermal heat source, and an industrial waste heat source. The additional heat source may include a heat exchanger, a heat pump, a power producing device, and any further combination of elements (e.g., piping and the like) suitable to form, provide, or deliver the necessary heat.

The method for heating a recirculating gas stream can further comprise one or more steps. For example, the gas stream G may be a stream exiting a turbine. As such, the pressure P<NUM> of gas stream G can be less than an earlier pressure P<NUM> of the gas stream before passage through the turbine. In some embodiments, P<NUM> can be substantially similar to P<NUM> (e.g., within <NUM>%, within <NUM>%, or within <NUM>% thereof). In some embodiments, recirculating gas stream Gc can be subjected to a superheating step after exiting the hot end of the heat exchanger (i.e., after being re-heated in the heat exchanger and receiving the additive heat of compression from G<NUM>). For example, recirculating gas stream Gc can be heated with heat of combustion, with solar heating, with nuclear heating, with geothermal heating, with industrial waste heating, or with any combination thereof. In some embodiments, recirculating gas stream Gc can be so-heated and then passed through a turbine for expansion and power production. The stream leaving the turbine may then be characterized again as gas stream G.

Claim 1:
A power generating system comprising:
a combustor (<NUM>) configured to exhaust a combustion stream;
a power production turbine (<NUM>) configured to receive and expand the combustion stream and form a turbine exhaust stream;
a first compressor (<NUM>; <NUM>) configured to receive a portion of the turbine exhaust stream and form a compressed recycle CO<NUM> stream;
a recuperative heat exchanger configured to receive the turbine exhaust stream and the compressed recycle CO<NUM> stream so that the compressed recycle CO<NUM> stream is heated with heat withdrawn from the turbine exhaust stream;
a first additive heating source arranged to provide heating for the compressed recycle CO<NUM> stream in addition to the heat withdrawn from the turbine exhaust stream, the first additive heat source comprising a second compressor (<NUM>) configured to receive and compress a portion of the turbine exhaust stream and form a compressed and heated stream for passage to the recuperative heat exchanger;
a pump (<NUM>) configured to receive the stream from the first compressor and the stream from the second compressor and pressurize the streams in combination, the pump (<NUM>) positioned downstream from the first compressor (<NUM>; <NUM>) and the second compressor (<NUM>); and
at least a second additive heating source arranged to heat the compressed recycle CO<NUM> stream in addition to the heat withdrawn from the turbine exhaust stream.