Patent Description:
One of the most challenging aspects of today's energy technologies is to effectively convert waste heat from a combustion process into useable power. Such power can be in the form of electrical or mechanical power for use in stationary and/or mobile applications.

Methods of converting waste heat into useful forms of energy are commonly referred to as bottoming cycles. Systems that utilize a bottoming cycle to provide power are referred to herein as bottoming cycle power systems.

Systems that utilize a fuel combustion process in an internal combustion engine (such as a piston engine or a turbine engine) as the motive force to drive a crankshaft for providing power are referred to herein as primary power systems. In most primary power systems the efficiency of the system ranges from below <NUM>% to a high of almost <NUM>%. This means that the majority of energy contained in the fuel is lost in the form of heat to the atmosphere through either the cooling circuit or exhaust of the internal combustion engine.

However, the waste energy contained in exhaust gas from the internal combustion engine of a primary power system may be utilized as the energy input for a bottoming cycle power system. If enough useful work can be recovered from such a bottoming cycle power system, the bottoming cycle power system could then be used to supplement the output of the primary power system for a more efficient overall system output.

One type of bottoming cycle is known as an inverted Brayton cycle. The inverted Brayton cycle typically includes an expansion turbine (or turbo-expander) that receives a flow of exhaust gas from a combustion process of an internal combustion engine. The exhaust gas carries a significant amount of heat energy. However the flow of exhaust gas is typically only at, or slightly above, atmospheric pressure. For example, the exhaust gas may exit the internal combustion engine at about <NUM>-<NUM> degrees Fahrenheit (F) (approximately <NUM>-<NUM> degrees Celsius (C)), but at only a few pounds per square inch (psi) (approximately a few tens of thousands of Pascals (Pa)) above atmospheric pressure. This makes recovering useful work difficult.

In the inverted Brayton cycle, the exhaust gas flows through a turbo-expander where it typically exits the turbo-expander at below atmospheric pressures (or vacuum pressures). The vacuum pressures are caused by a compression turbine (or turbo-compressor), which is the final step in the inverted Brayton cycle. That is, the exhaust gas enters the turbo-compressor where it may be pumped back to atmospheric pressure. The amount of energy recovered from an inverted Brayton cycle is the energy produced by the turbo-expander minus the energy consumed by the turbo-compressor. Therefore, the less work needed by the turbo-compressor to compress the expanded volume of exhaust gas, the greater the net-work produced from the inverted Brayton cycle.

Various prior art cooling systems can be utilized to reduce the specific volume of exhaust gas prior to entering the turbo-compressor in an inverted Brayton cycle and, therefore, reduce the amount of work required by the turbo-compressor to compress the exhaust gas. Problematically however, these cooling systems consume a significant amount of energy due to pumps and/or other energy consuming devices needed to circulate coolants through the cooling system.

Moreover, the more the exhaust gas is cooled in order to produce as much net-work from the inverted Brayton cycle (or other bottoming cycles) as possible, the more the density of the cooled exhaust gas will increase. Problematically, if the exhaust gas is cooled to ambient or near ambient temperatures, the exhaust gas will become too dense to flow up the required stack of the internal combustion engine. In that case, the exhaust gas must be re-heated as it exits the turbo-compressor, which may significantly reduce the amount of net-work that the inverted Braytoncycle can provide.

For example, <CIT> describes a bottoming cycle power system which utilises an inverted Brayton cycle comprising an expander and a compressor both mounted on a crankshaft, along with an absorption chiller for a two-stage cooling process. This cooling process reduces the volume and mass of exhaust gases moving from the expander to the compressor.

Further, the exhaust gas of an internal combustion engine contains a significant amounts of water vapor and carbon dioxide as naturally occurring by-products of the combustion process. Problematically, the water vapor has a relatively high specific volume and mass, which causes an unwanted burden on the compression work of the compressor in the inverted Brayton cycle. Also problematically, prior art carbon dioxide capture systems generally consume a significant amount of energy to remove the carbon dioxide from the exhaust gas, which would also cause a burden on the efficiency of the internal combustion engine.

Accordingly, there is a need for a bottoming cycle power system, such as an inverted Brayton bottoming cycle power system, wherein the specific volume of flow of exhaust gas is significantly and efficiently reduced after exiting the turbo-expander and prior to entering the turbo-compressor. More specifically, there is a need to reduce the work required of the turbo-compressor in a bottoming cycle power system to increase the overall efficiency of that bottoming cycle power system.

Further there is a need to efficiently decrease the volume and mass of water vapor in a flow of exhaust gas prior to entering the turbo-compressor of a bottoming cycle power system. Additionally, there is a need to efficiently re-heat exhaust gas that has been cooled to ambient or near ambient temperatures, in order to enable the exhaust gas to flow up an internal combustion engine's stack with little drain on the net-work of the associated bottoming cycle power system. Additionally, there is a need to reduce the energy required in any carbon dioxide capture system used to remove the carbon dioxide from exhaust gas and, therefore, help to maintain the efficiency of the internal combustion engine associated with the bottoming cycle power system.

A bottoming power cycle according to the invention is described in claim <NUM> and the corresponding method of generating electrical power according to the invention is described in claim <NUM>. The present invention offers advantages and alternatives over the prior art by providing a bottoming cycle power system for receiving a flow of exhaust gas from a combustion process. The bottoming cycle power system includes an exhaust gas heat exchanger that has a first and a second flow path. The first flow path receives hot exhaust gas after it has exited the turbo-expander and prior to entering the turbo-compressor of the bottoming cycle power system. The second flow path receives cooled exhaust gas after it has exited the turbo-compressor. The cooled exhaust gas provides a first stage of cooling of the hot exhaust gas as it passes through the exhaust gas heat exchanger. An exhaust gas processing system is disposed between the exhaust gas heat exchanger and the turbo-compressor to provide at least a second stage of cooling of the exhaust gas prior to entering the turbo-compressor.

A bottoming cycle power system in accordance with one or more aspects of the present invention includes a turbine-generator. The turbine-generator includes a turbo-expander and turbo-compressor disposed on a turbo-crankshaft. The turbo-expander is operable to rotate the turbo-crankshaft as a flow of exhaust gas from a combustion process passes through the turboexpander. The turbo-compressor is operable to compress the flow of exhaust gas after the exhaust gas passes through the turbo-expander. An exhaust gas heat exchanger includes first and second flow paths operable to exchange heat therebetween. The first flow path is operable to receive the flow of exhaust gas from the turbo-expander prior to the exhaust gas being compressed by the turbo-compressor. The second flow path is operable to receive the flow of exhaust gas from the turbo-compressor after the exhaust gas has been compressed by the turbo-compressor. An exhaust gas processing system is operable to receive and cool the flow of exhaust gas after the exhaust gas has passed through the first flow path of the exhaust gas heat exchanger and prior to the exhaust gas being compressed by the turbo-compressor. The exhaust gas processing system comprises at least one of a cooling tower, a cooling tower heat exchanger, an absorption chiller, an absorption chiller heat exchanger, a dehumidifier system and a vapor-compression refrigeration system.

A combined power system in accordance with one or more aspects of the present invention includes a primary power system and a bottoming cycle power system. The primary power system includes an internal combustion engine having a rotatable crankshaft. The engine is operable to use fuel in a combustion process to deliver primary power to the engine crankshaft. The combustion process produces a flow of exhaust gas. The bottoming cycle power system is as described above.

A bottoming cycle power system in accordance with one or more aspects of the present invention may further comprise a carbon dioxide capture system. The carbon dioxide capture system comprises a first capture tank, a second capture tank, a carbon dioxide compressor and a compressor coolant loop. Each capture tank contains carbon dioxide absorbent material operable to absorb carbon dioxide from a flow of exhaust gas. The first and second capture tanks each include an exhaust gas inlet port, an exhaust gas outlet port and a carbon dioxide outlet port. The exhaust gas inlet port of each capture tank is selectively connectable to the flow of exhaust gas prior to the exhaust gas passing through the carbon dioxide absorbent material. The exhaust gas outlet port of each capture tank is selectively connectable to the flow of exhaust gas after the flow of exhaust gas has passed through carbon dioxide absorbent material. The carbon dioxide compressor is selectively connectable to the carbon dioxide outlet port of either the first or second capture tank. The carbon dioxide compressor is operable to pump carbon dioxide out of the carbon dioxide outlet port that the carbon dioxide compressor is connected to. The compressor coolant loop is selectively connectable between the carbon dioxide compressor and the first capture tank or between the carbon dioxide compressor and the second capture tank. The compressor coolant loop is operable to flow a compressor coolant fluid to remove heat of compression from the compressor and to transfer the heat of compression to the first or second capture tank. The heat of compression is operable to release a portion of the carbon dioxide absorbed by the carbon dioxide absorbent material in the first or second capture tank.

Certain examples will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the methods, systems, and devices disclosed herein. One or more examples are illustrated in the accompanying drawings. Those skilled in the art will understand that the methods, systems, and devices specifically described herein and illustrated in the accompanying drawings are non-limiting examples and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one example maybe combined with the features of other examples.

The terms "significantly", "substantially", "approximately", "about", "relatively," or other such similar terms that may be used throughout this disclosure, including the claims, are used to describe and account for small fluctuations, such as due to variations in processing from a reference or parameter. Such small fluctuations include a zero fluctuation from the reference or parameter as well. For example, they can refer to less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%, such as less than or equal to ± <NUM>%.

Referring to <FIG>, a schematic is depicted of an example of a combined power system <NUM> having a primary power system <NUM> and a bottoming cycle power system <NUM>, wherein the bottoming cycle power system <NUM> includes a turbine generator <NUM>, an exhaust gas heat exchanger <NUM> and an exhaust gas processing system <NUM>, in accordance with the present invention. In this example, the bottoming cycle power system <NUM> is an inverted Brayton bottoming cycle power system <NUM>.

In this specific example, the combined power system <NUM>, primary power system <NUM> and bottoming cycle power system <NUM> are configured to generate electrical power to, for example, a grid (i.e., an interconnect network for delivering electricity from producers to consumers). However, it is within the scope of the present invention, that the power systems <NUM>, <NUM> and <NUM> could be used to provide mechanical power as well.

Moreover, such power systems of the present invention may be used in both stationary
applications and mobile applications. Examples of such stationary applications include electric generator systems for delivering electric power to a grid, electric generator systems for delivering electric power to a building, mechanical power systems for delivering mechanical power for an industrial manufacturing process or the like. Examples of such mobile applications include mechanical power systems for delivering mechanical power to a motor vehicle, electrical power systems for delivering electrical power to an electric vehicle or the like.

The primary power system <NUM> includes an internal combustion engine <NUM> having an engine crankshaft <NUM> that is operatively connected to a primary electric generator <NUM>. The internal combustion engine <NUM> may include a turbine engine, a piston engine or similar. The engine <NUM> utilizes fuel in a combustion process as the motive force that rotates the engine crankshaft <NUM> and the primary electric generator <NUM> to generate a first electrical output <NUM>. Additionally, the combustion process produces a flow of exhaust gas <NUM>, which may be routed to the bottoming cycle power system <NUM>. The flow of exhaust gas from the combustion process of the internal combustion engine <NUM> may be at, or near, atmospheric pressure and may have a temperature in the range of <NUM> to <NUM> degrees (F) (approximately <NUM> to <NUM> degrees C).

Though in this example, the combustion process and associated the flow of exhaust gas <NUM> is utilized within a primary power system <NUM>, other devices and/or systems may utilize a combustion process to produce exhaust gas <NUM>. For example, the exhaust gas may be produced from a furnace system, or from burning natural gas at an oil well site or the like.

The bottoming cycle power system <NUM> includes a turbine generator <NUM>. The turbine generator <NUM> includes a turbo-expander <NUM> and turbo-compressor <NUM> disposed on a turbo-crankshaft <NUM>. The turbo-expander <NUM> is operable to receive and expand the flow of exhaust gas <NUM> from the combustion process of the internal combustion engine <NUM>. The turbo-expander <NUM> is operable to rotate the turbo-crankshaft <NUM> as the exhaust gas <NUM> passes through the turboexpander <NUM>. The turbo-expander <NUM> expands the exhaust gas <NUM> to extract energy from the exhaust gas <NUM> and convert the energy to work on the crankshaft <NUM>. Because the exhaust gas <NUM> is expanded as it passes through the turbo-expander <NUM>, the exhaust gas <NUM> will be under a vacuum as it exits the turbo-expander <NUM>, for example, at a vacuum pressure of perhaps <NUM> atmospheres (approximately <NUM> kPa). Additionally, the exhaust gas <NUM> will cool as it performs work on the crankshaft, for example within a range of <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C).

The turbo-compressor <NUM> (typically a turbine compressor or similar) is operatively connected to the flow of exhaust gas <NUM>. More specifically, as the turbo-compressor <NUM> is rotated by the turbo-crankshaft <NUM>, the turbo-compressor is operable to compress the flow of exhaust gas <NUM> after the exhaust gas passes through the turbo-expander <NUM>, the exhaust gas heat exchanger <NUM> and the exhaust gas processing system <NUM>.

Additionally, the turbo-compressor <NUM> pulls a vacuum on the output side of the turboexpander <NUM> (for example a vacuum of about <NUM> atmospheres (approximately 20kPa)) to increase a pressure difference across the turbo-expander <NUM>. The increased pressure difference enhances the expansion of the flow of exhaust gas <NUM> through the turbo-expander <NUM> in order to convert as much energy in the exhaust gas <NUM> into usable work on the turbo-crankshaft <NUM>.

A bottoming cycle generator <NUM> is also disposed on the turbo-crankshaft <NUM>. The bottoming cycle generator <NUM> is operable to generate electrical power when the turbo-crankshaft <NUM> is rotated by the turbo-expander <NUM>. In other words, the bottoming cycle generator <NUM> generates a second electrical output <NUM> that may be used to supplement the first electrical output <NUM> of the primary power system <NUM>.

The exhaust gas <NUM> flows from the turbo-expander <NUM> into the exhaust gas heat exchanger <NUM>. The exhaust gas heat exchanger <NUM> includes a first flow path <NUM> and a second flow path <NUM> operable to exchange heat therebetween. More specifically, the first flow path <NUM> is operable to transfer heat into the second flow path <NUM>. The first flow path <NUM> is operable to receive the flow of exhaust gas <NUM> from the turbo-expander <NUM> prior to the exhaust gas <NUM> being compressed by the turbo-compressor <NUM>. The second flow path <NUM> is operable to receive the flow of exhaust gas <NUM> from the turbo-compressor <NUM> after the exhaust gas <NUM> has been compressed by the turbo-compressor <NUM>.

As will be explained in greater detail herein, the hot exhaust gas <NUM> from the turboexpander <NUM> (for example at about a temperature of <NUM>-<NUM> degrees F(approximately <NUM>-<NUM> degrees C)), that flows through the first flow path <NUM> of the exhaust gas heat exchanger <NUM>, is cooled by the much cooler exhaust gas <NUM> (for example at about a temperature range of <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C) from the turbo-compressor <NUM>, that flows through the second flow path <NUM> of the exhaust gas heat exchanger <NUM>.

Advantageously, the cooled exhaust gas <NUM> from the turbo-compressor <NUM> provides a first stage of cooling for the hotter exhaust gas <NUM> from the turbo-expander <NUM>. For example, the exhaust gas <NUM> may be cooled down to about a range of <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C) as it exits the first path <NUM> of the exhaust gas heat exchanger <NUM>.

Also, advantageously, the hotter exhaust gas <NUM> from the turbo-expander <NUM> reheats the cooler exhaust gas <NUM> from the turbo-compressor <NUM> to temperatures that enable the exhaust gas <NUM> to flow readily up a stack <NUM> (see <FIG>) of the combined power system <NUM>. For example, the exhaust gas <NUM> exiting the second path <NUM> of the gas heat exchanger <NUM> may be within a range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C).

The stack <NUM>, as used herein, will refer to the extended exhaust piping system designed to route exhaust gas away from the source of the combustion process (in this example, the source of the combustion process is the internal combustion engine <NUM>). In this example, the stack <NUM> of the combined power system <NUM> is designed to route the flow of exhaust gas <NUM> away from the combined power system <NUM> after the exhaust gas exits the second path <NUM> of the exhaust gas heat exchanger <NUM> (see <FIG>).

The stack <NUM> of the combined power system <NUM> is required to route the exhaust gas <NUM> away from the combined power system <NUM> and to maintain air quality in the proximity of the combined power system <NUM>. The stack <NUM>, by regulation, may have a minimum height that may be as much as <NUM> times the height of a building or container that houses the engine <NUM> or more. If the exhaust gas <NUM> is too cool (for example, near or below ambient temperature), the exhaust gas <NUM> will be too dense to readily flow to the top of the stack <NUM>. As will be explained in greater detail herein, cooling the exhaust gas <NUM> to near ambient temperature before it enters the turbo-compressor <NUM> is advantageous for increasing the compression ratio (and therefore efficiency) across the turbo-expander <NUM>. However, reheating the exhaust gas <NUM> to temperatures that are significantly higher than ambient temperature after the exhaust gas <NUM> exits the turbo-compressor <NUM> is advantageous for routing the exhaust gas <NUM> up the stack <NUM>. The exhaust gas heat exchanger <NUM> helps to perform both of these functions.

The exhaust gas processing system <NUM> is operable to receive and cool the flow of exhaust gas <NUM> after the exhaust gas <NUM> has passed through the first flow path <NUM> of the exhaust gas heat exchanger <NUM> and prior to the exhaust gas <NUM> being compressed by the turbo-compressor <NUM>. The exhaust gas processing system <NUM> provides a second stage of cooling for the exhaust gas <NUM> prior to the exhaust gas <NUM> entering the turbo-compressor <NUM>.

Referring to <FIG>, a schematic of an example is depicted of the combined power system <NUM> of <FIG> further including a carbon dioxide capture system <NUM>, in accordance with the present invention. The carbon dioxide capture system <NUM> is operable to remove and capture carbon dioxide <NUM> from the exhaust gas <NUM> after the exhaust gas <NUM> exits the turbo-compressor <NUM> and prior to the exhaust gas <NUM> flowing through the second flow path <NUM> of the exhaust gas heat exchanger <NUM>. As will be explained in greater detail herein, the carbon dioxide capture system <NUM> is also operable to advantageously regenerate the captured carbon dioxide <NUM> using a heat of compression of a carbon dioxide compressor <NUM> (see <FIG>).

Referring to <FIG>, a schematic is depicted of an example of the combined power system <NUM> of <FIG>, with a more detailed example of the exhaust gas processing system <NUM> and the carbon dioxide capture system <NUM>, in accordance with the present invention. The exhaust gas
processing system <NUM> performs at least a second stage of cooling on the exhaust gas <NUM> after the exhaust gas <NUM> exits the exhaust gas heat exchanger <NUM>. However, the exhaust gas processing system <NUM> may perform other functions as well. For example, the exhaust gas processing system <NUM> may perform several stages of cooling and/or may remove water from the flow of exhaust gas <NUM>.

In the specific example depicted in <FIG>, the exhaust gas process system <NUM> includes a cooling tower heat exchanger <NUM>, an absorption chiller heat exchanger <NUM> and a dehumidifier system <NUM> that process the exhaust gas <NUM> as it passes through the exhaust gas processing system <NUM>. The cooling tower heat exchanger <NUM> performs a second stage of cooling on the exhaust gas <NUM>, the absorption chiller heat exchanger <NUM> performs a third stage of cooling on the exhaust gas <NUM> and the dehumidifier system <NUM> removes water from the exhaust gas <NUM> prior to the exhaust gas entering the turbo-compressor <NUM>.

The cooling tower heat exchanger <NUM> is operable to receive the flow of exhaust gas <NUM> from the exhaust gas heat exchanger <NUM>. The cooling tower heat exchanger <NUM> is operable to cool the exhaust gas <NUM> with a flow of cooling tower coolant fluid <NUM> (see <FIG>) that flows in a cooling tower coolant loop <NUM> between a cooling tower <NUM> and the cooling tower heat exchanger <NUM>. In this specific example, the cooling tower coolant fluid is water, but may also be other coolants, such as glycol or the like. The cooling tower heat exchanger <NUM>, may, for example, cool the exhaust gas down to a temperature range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C).

From the cooling tower heat exchanger <NUM>, the exhaust gas <NUM> flows to the absorption chiller heat exchanger <NUM>. The absorption chiller heat exchanger <NUM> is operable to receive the flow of exhaust gas <NUM> from the exhaust gas heat exchanger <NUM> and to cool the exhaust gas <NUM> with a flow of absorption chiller coolant fluid (such as water, glycol or the like) that flows in an absorption chiller coolant loop <NUM> between an absorption chiller <NUM> and the absorption chiller heat exchanger <NUM>. For example, the absorption chiller heat exchanger <NUM> may cool the exhaust gas <NUM> down to a range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C).

A coolant pump <NUM> may be used to pump the absorption chiller coolant fluid around the absorption chiller coolant loop <NUM>. An expansion tank <NUM> may be used to provide room for thermal expansion of the absorption chiller coolant fluid as it is circulated around the absorption chiller coolant loop <NUM>.

The absorption chiller <NUM> may be powered by the heat energy from an engine coolant loop <NUM> of the internal combustion engine <NUM>. More specifically, engine coolant fluid may be circulated in the engine coolant loop <NUM>, via a coolant pump <NUM>, between a generator section <NUM> (see <FIG>) of the absorption chiller <NUM> and the engine <NUM>.

Additionally, a water tower <NUM> may be used to remove heat energy from the absorption chiller <NUM>. More specifically, a water tower <NUM> may circulate a flow of water tower coolant fluid (such as water, glycol or the like) in a water tower coolant loop <NUM> between the water tower <NUM> and the absorption chiller <NUM> to remove heat from an evaporator section <NUM> (see <FIG>) and an absorption section <NUM> (see <FIG>) of the absorption chiller <NUM>.

In the specific example illustrated in <FIG>, the exhaust gas <NUM> flows from the cooling tower heat exchanger <NUM> directly into the absorption chiller heat exchanger <NUM>. However, other examples of the exhaust gas processing system <NUM> are within the scope of this disclosure. For example, the exhaust gas <NUM> may flow into the absorption chiller heat exchanger <NUM> first and then into the cooling tower heat exchange <NUM>. Alternatively, there may be only an absorption chiller heat exchanger <NUM> or only a cooling tower heat exchanger <NUM> in the exhaust gas processing system <NUM>.

Additionally, there may be other types of cooling systems utilized to cool the exhaust gas <NUM> in lieu of, or in place of, the cooling tower heat exchanger <NUM> and absorption chiller heat exchanger <NUM>. For example, various types of vapor-compression refrigeration systems (not shown) may be utilized to cool the exhaust gas <NUM> in the exhaust gas processing system <NUM>.

From the absorption chiller heat exchanger <NUM>, the exhaust gas <NUM> may optionally flow through the dehumidifier system <NUM>. The dehumidifier system <NUM> is operable to remove a substantial amount of water from the exhaust gas <NUM>. The dehumidifier system may use various water absorption materials (for example lithium bromide, activated charcoal, calcium chloride, zeolites or other types of hygroscopic substances) to absorb water <NUM> from the exhaust gas <NUM>. The water <NUM> may be pumped away from the dehumidifier system <NUM> via water pump <NUM>. Though this particular example of an exhaust gas processing system <NUM> includes a dehumidifier system <NUM>, it is within the scope of this invention that a dehumidifier system not be utilized in
the exhaust gas processing system <NUM>.

From the dehumidifier system <NUM>, the exhaust gas <NUM> flows into the turbo-compressor <NUM>. At this stage of exhaust gas flow <NUM>, the temperature of the exhaust gas <NUM> has been reduced to near ambient temperatures. The near ambient temperature of the exhaust gas <NUM> enables the turbo-compressor <NUM> to efficiently pump the exhaust gas <NUM> back to atmospheric pressure or greater with a reduced work burden on the turbo-expander <NUM>. For example, the exhaust gas entering the turbo-compressor <NUM> may be within a temperature range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C) and may be within a pressure range of about <NUM> atmospheres (approximately 20kPa) or less, while the exhaust gas <NUM> exiting the turbo-compressor <NUM> may be within a temperature range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C) and may have an atmospheric pressure of about <NUM> to <NUM> atmospheres (approximately 150kPa to 200kPa).

By reducing the work burden of the turbo-compressor <NUM> on the turbo-expander <NUM>, the net energy produced by the bottoming cycle generator <NUM> is increased significantly. Additionally, the components in the exhaust gas processing system <NUM> (such as the cooling towers <NUM>, <NUM>, the cooling tower heat exchanger <NUM>, the absorption chiller <NUM>, the absorption chiller heater exchanger <NUM> and the dehumidifier system <NUM>) are selected to consume the least amount of operating power and provide the least amount of exhaust gas pressure drop through the exhaust gas processing system. By doing so, the second electrical output <NUM> power of the bottoming cycle generator <NUM> is maximized.

As such, the second electrical output <NUM> of the bottoming cycle generator <NUM> may be operable to provide a significant portion of electric power required to operate the exhaust gas processing system <NUM>. Additionally, the second electrical output <NUM> of the bottoming cycle generator <NUM> may be operable to provide all electric power required to operate the exhaust gas processing system <NUM>. Additionally, the second electrical output <NUM> of the bottoming cycle generator <NUM> may be operable to provide a portion of electric power required to operate the exhaust gas processing system <NUM> and the carbon dioxide capture system <NUM>. Additionally, the second electrical output <NUM> of the bottoming cycle generator <NUM> may be operable to provide all electric power required to operate the exhaust gas processing system <NUM> and the carbon dioxide capture system <NUM>.

After the exhaust gas <NUM> exits the turbo-compressor <NUM>, the exhaust gas <NUM> is routed through the carbon dioxide capture system <NUM>. For purposes of clarity, the functional details of the carbon dioxide capture system <NUM> will be discussed in greater detail with reference to <FIG>.

From the carbon dioxide capture system <NUM>, the exhaust gas <NUM> flows through the second path <NUM> of the exhaust gas heat exchanger <NUM>. The cooled exhaust gas <NUM> passing through the second path <NUM> is reheated by the hot exhaust gas <NUM> passing through the first path <NUM> of the exhaust gas heat exchanger <NUM>. The reheated exhaust gas <NUM> exiting the second path <NUM> is significantly above ambient temperatures (for example, <NUM> to <NUM> degrees F (approximately <NUM> to <NUM> degrees C)) and is significantly less dense than the ambient air. Accordingly, the reheated exhaust gas <NUM> may readily flow up the stack <NUM> of the combined power system <NUM>.

Referring to <FIG>, a schematic is depicted of an example of a more detailed view of the absorption chiller heat exchanger <NUM> and associated absorption chiller <NUM> that may be utilized in the exhaust gas processing system of <FIG>, in accordance with the present invention.

The absorption chiller <NUM> has a generator section <NUM>, a condenser section <NUM>, an evaporator section <NUM> and an absorption section <NUM> all in fluid communication with each other and operable to circulate an absorption chiller refrigerant <NUM> (in this example, water) therethrough. The generator section <NUM> has a generator section heat exchanger <NUM> to receive the flow of heated engine coolant fluid that flows in the engine coolant loop <NUM> between the generator section heat exchanger <NUM> and the internal combustion engine <NUM>. The generator section heat exchanger <NUM> is operable to evaporate the absorption chiller refrigerant <NUM> to remove heat from the engine coolant fluid, which may enter the generator section heat exchanger at about <NUM> degrees F(approximately <NUM> degrees C).

More specifically in this example, the heat from the hot engine coolant evaporates the water-refrigerant <NUM> from a dilute brine solution of water and lithium bromide. The evaporated water <NUM> then flows to the condenser section <NUM>.

The condenser section <NUM> is operable to condense the absorption chiller refrigerant <NUM> utilizing the water tower coolant loop <NUM> of the water tower <NUM>. The condensed water <NUM> flows through an orifice <NUM> to drop its pressure as the water <NUM> enters the evaporator section <NUM>.

The evaporator section <NUM> has an evaporator section heat exchanger <NUM> to receive the absorption chiller coolant fluid from the absorption chiller heat exchanger <NUM>. The evaporator section heat exchanger <NUM> is operable to remove heat from the absorption chiller coolant fluid by re-evaporating the water <NUM> condensed in the condenser section <NUM> to produce steam (i.e., evaporated absorption chiller refrigerant) <NUM>.

The steam then flows to the absorption section <NUM>, which contains a concentrated solution of brine that is operable to re-condense the water <NUM> utilizing the water tower coolant loop <NUM> of the water tower <NUM>. An absorption chiller refrigerant pump <NUM> pumps the concentrated brine back to the generator section <NUM> to complete the absorption chiller refrigeration cycle.

Referring to <FIG>, a schematic is depicted of an example of a more detailed view of the cooling tower heat exchanger <NUM> and associated cooling tower <NUM> that may be utilized in the exhaust gas processing system of <FIG>, in accordance with the present invention. In this specific
example, the cooling tower coolant fluid <NUM> that flows through the cooling tower coolant loop <NUM> is water. However, other cooling tower coolant fluids may also be used or included with the water, such as, for example, glycol or the like.

During operation, a cooling tower coolant pump <NUM> may be used to circulate the water (cooling tower coolant fluid) <NUM> through the cooling tower coolant loop <NUM> between the cooling tower heat exchange and the water tower <NUM>. The water <NUM> from the water tower <NUM> may enter the exhaust gas heat exchanger <NUM> in a range of about <NUM> to <NUM> degrees F (approximately <NUM> to <NUM> degrees C). The exhaust gas <NUM> may enter the exhaust gas heat exchanger <NUM> in a range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C). The water <NUM> will cool the exhaust gas <NUM> as the water and exhaust gas pass through the cooling tower heat exchanger <NUM>. For example, the exhaust gas <NUM> may be cooled down to a range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C) and the water may be heated up to a temperature range of about <NUM>-<NUM> degrees F (approximately <NUM>-<NUM> degrees C) as both the water <NUM> and exhaust gas <NUM> pass through the cooling tower heat exchanger <NUM>.

After passing through the cooling tower heat exchanger <NUM>, the heated water <NUM> will return to the upper portion <NUM> of the cooling tower <NUM> where the water enters the cooling tower's coolant distribution system <NUM>. The distribution system <NUM> will route the water <NUM> through a plurality of cooling tower nozzles <NUM>, which will spray the water onto a fill material <NUM>. The fill material (or fill media) <NUM> is a material used to increase the surface area of the cooling tower <NUM>. The fill material <NUM> may be, for example, knitted metal wire, ceramic rings or other materials that provide a large surface area when positioned or packed together within the cooling tower <NUM>. The fill material <NUM> slows the water <NUM> down and exposes a large amount of water surface area to air-water contact.

Ambient air <NUM> is pulled through a lower portion <NUM> of the cooling tower <NUM> and out the upper portion <NUM> of the cooling tower <NUM> via a cooling tower fan <NUM>. A small amount of water <NUM> evaporates as the air <NUM> and water <NUM> contact each other in the fill material <NUM>, which cools the water. For example, the water <NUM> may be cooled down to a range of about <NUM> to <NUM> degrees F (approximately <NUM> to <NUM> degrees C).

The cooled water <NUM> falls into a collection basin <NUM>, which adds back make-up water to compensate for the small amount of water that has been evaporated during the evaporative cooling process. The cooled water <NUM> is then pumped through the cooling tower coolant loop <NUM> and back to the cooling tower heat exchanger <NUM> via the cooling tower coolant pump <NUM> to complete the refrigeration cycle.

The cooling tower <NUM> may be one of several types of cooling towers, such as crossflow cooling towers, counterflow cooling towers, open loop cooling towers, closed loop cooling towers or the like. However, they most often operate utilizing evaporative cooling produced from air to cooling tower coolant fluid (e.g., water) contact.

Referring to <FIG>, a schematic is depicted of an example of an enlarged view of the carbon dioxide capture system <NUM> utilized in the combined power system <NUM> of <FIG>, in accordance with the present invention. As the exhaust gas <NUM> exits the turbo-compressor <NUM> it
will undesirably contain carbon dioxide <NUM>. To remove the carbon dioxide <NUM> prior to entering the exhaust gas heat exchanger <NUM>, the carbon dioxide capture system <NUM> may be utilized.

The carbon dioxide capture system <NUM> includes a first capture tank <NUM> and a second capture tank <NUM>. Each capture tank <NUM>, <NUM> contains carbon dioxide absorbent material <NUM> operable to absorb carbon dioxide <NUM> from the exhaust gas <NUM>. The carbon dioxide absorbent material may be zeolite, metal organic frameworks material, calcium hydroxide or the like.

The first and second capture tanks <NUM>, <NUM> each include an exhaust gas inlet port 208A and 208B, which are selectively connectable to the flow of exhaust gas <NUM> from the turbo-compressor <NUM>. In other words, the exhaust gas inlet ports 208A and 208B are selectively connectable to the flow of exhaust gas prior to the exhaust gas passing through the carbon dioxide absorbent material. More specifically, flow valve 210A controls flow of exhaust gas <NUM> into the exhaust gas inlet port 208A of the first capture tank <NUM> and flow valve 210B controls flow of exhaust gas <NUM> into the exhaust gas inlet port 208B of the second capture tank <NUM>.

The first and second capture tanks <NUM>, <NUM> also include an exhaust gas outlet port 212A and 212B, which are selectively connectable to the second flow path <NUM> of the exhaust gas heat exchanger <NUM>. In other words, the exhaust gas outlet ports 212A and 212B are selectively connectable to the flow of exhaust gas after the flow of exhaust gas has passed through carbon dioxide absorbent material. More specifically, flow valve 214A controls flow of exhaust gas <NUM> out of the exhaust gas outlet port 212A of the first capture tank <NUM> and into the second flow path <NUM> of the exhaust gas heat exchanger <NUM>. Additionally, flow valve 214B controls flow of exhaust gas <NUM> out of the exhaust gas outlet port 212B of the second capture tank <NUM> and into the second flow path <NUM> of the exhaust gas heat exchanger <NUM>.

The first and second capture tanks <NUM>, <NUM> also include a carbon dioxide outlet port 216A and 216B, which are selectively connectable to a carbon dioxide compressor <NUM>. More specifically, flow valve 218A controls flow of regenerated carbon dioxide <NUM> out of the carbon dioxide outlet port 216A of the first capture tank <NUM> and into the carbon dioxide compressor <NUM>. Additionally, flow valve 218B controls flow of regenerated carbon dioxide <NUM> out of the carbon dioxide outlet port 216B of the second capture tank <NUM> and into the carbon dioxide compressor <NUM>. The carbon dioxide compressor <NUM> is operable to pump carbon dioxide <NUM> out of the carbon dioxide outlet ports 216A, 216B that the carbon dioxide compressor <NUM> is connected to. The carbon dioxide compressor <NUM> may be a rotary screw type compressor, a piston compressor or the like.

A compressor coolant loop <NUM> is selectively connectable between the carbon dioxide compressor <NUM> and the first capture tank <NUM> or between the carbon dioxide compressor <NUM> and the second capture tank <NUM>. The compressor coolant loop <NUM> is operable to flow a compressor coolant fluid <NUM> (such as water, glycol of the like) to remove a heat of compression from the compressor <NUM> and to transfer the heat of compression to the first or second capture tanks <NUM>, <NUM>. The heat of compression is operable to release a portion of the carbon dioxide <NUM> absorbed by the carbon dioxide absorbent material <NUM> in the first or second capture tanks <NUM>, <NUM>.

More specifically, the compressor coolant loop <NUM> includes a compressor coolant jacket <NUM> of the compressor <NUM>, a first capture tank heating jacket <NUM> of the first capture tank <NUM> and a second capture tank heating jacket <NUM> of the second capture tank <NUM>. The compressor coolant jacket <NUM> is operable to contain and circulate the compressor coolant fluid <NUM> around the outer surface of the compressor <NUM> to cool the compressor <NUM>. The compressor coolant fluid <NUM> will remove the heat of compression from the compressor <NUM>.

For purposes herein, a heating or coolant jacket (such as coolant jacket <NUM>, and heating jackets <NUM> and <NUM>) may refer to an outer casing or system of tubing, which holds fluid and through which the fluid circulates to cool or heat a vessel or device. For example, the compressor coolant jacket <NUM> may be a casing which surrounds the carbon dioxide compressor <NUM> to enable the coolant fluid to absorb the heat of compression and to cool the compressor <NUM>. Also, the first and second capture tank heating jackets <NUM> and <NUM> may be casings or systems of tubing, which are operable to transfer the heat of compression to the selected first or second capture tanks <NUM>, <NUM> and to heat the carbon dioxide <NUM> captured within the selected tank <NUM>, <NUM>.

The heating jackets <NUM> and <NUM> are operable to selectively contain and circulate the compressor coolant fluid <NUM> (which is heated with the heat of compression from compressor <NUM>) around the outer surfaces of the first or second capture tanks <NUM>, <NUM> respectively to heat the selected capture tank <NUM>, <NUM>. The compressor coolant fluid <NUM> will add the heat of compression to the selected capture tank <NUM>, <NUM>. The heat of compression from the compressor <NUM> will then advantageously be used to regenerate (or desorb) a portion, or substantially all, of the carbon dioxide <NUM> from the carbon dioxide absorbent material <NUM> so that it can be pumped by the compressor <NUM> into a holding tank <NUM> for later use and/or disposal.

A carbon dioxide heat exchanger <NUM> may be disposed between the holding tank <NUM> and the carbon dioxide compressor <NUM> to cool the carbon dioxide <NUM> prior to entering the holding tank <NUM>. The carbon dioxide heat exchanger <NUM> may be cooled by a cooling tower <NUM> that circulates coolant fluid between the cooling tower <NUM> and the carbon dioxide heat exchanger <NUM> via carbon dioxide heat exchanger coolant loop <NUM>.

The compressor coolant fluid <NUM> is pumped around the compressor coolant loop <NUM> via pump <NUM>. Flow valves <NUM>, <NUM>, <NUM> and <NUM> control the flow of compressor coolant fluid <NUM> to either the first capture tank <NUM> or second capture tank <NUM>. More specifically, when valves <NUM> and <NUM> are open, and valves <NUM> and <NUM> are closed, the coolant loop <NUM> circulates the coolant fluid <NUM> via pump <NUM> between the compressor <NUM> and the first capture tank <NUM>. In this configuration, the compressor <NUM> is cooled and the first capture tank <NUM> is heated. When the valves <NUM> and <NUM> are closed, and valves <NUM> and <NUM> are open, the coolant loop <NUM> circulates the coolant fluid <NUM> via pump <NUM> between the compressor <NUM> and the second capture tank <NUM>. In this configuration, the compressor <NUM> is cooled and the second capture tank <NUM> is heated.

During operation, the various flow valves may be configured such that the exhaust gas inlet port 208A of the first capture tank <NUM> is connected (i.e., in fluid communication) to the flow of exhaust gas <NUM> from the turbo-compressor <NUM>. In other words, the exhaust gas inlet port 208A is connected to the flow of exhaust gas <NUM> prior to the exhaust gas <NUM> passing through the carbon dioxide absorbent material <NUM>. Additionally, the first capture tank's exhaust gas outlet port 212A is connected (i.e., in fluid communication) to the second flow path <NUM> of the exhaust gas heat exchanger <NUM>. In other words, the exhaust gas outlet port 212A is connected to the flow of exhaust gas <NUM> after the exhaust gas has passed through the carbon dioxide absorbent material <NUM>. Additionally, the carbon dioxide compressor <NUM> may be connected to the carbon dioxide outlet port 216B of the second capture tank <NUM> and the compressor coolant loop <NUM> may be connected between the carbon dioxide compressor <NUM> and the second capture tank <NUM>. In this configuration, exhaust gas <NUM> will flow into the first capture tank <NUM> to remove the carbon dioxide <NUM> from the exhaust gas <NUM> flow prior to entering the exhaust gas heat exchanger <NUM>. Simultaneously, the heat of compression from the carbon dioxide compressor <NUM> will advantageously be used to heat the second capture tank <NUM> to regenerate the carbon dioxide from the second capture tank <NUM> and to pump the carbon dioxide <NUM> into the holding tank <NUM>. By using the heat of compression of the carbon dioxide compressor <NUM> to regenerate the carbon dioxide in the second capture tank <NUM>, the energy needed from external sources (such as electric heaters or the like) to regenerate the carbon dioxide is advantageously reduced.

Claim 1:
A bottoming cycle power system (<NUM>) comprising:
a turbine-generator (<NUM>) comprising a turbo-expander (<NUM>) and turbo-compressor (<NUM>) disposed on a turbo-crankshaft (<NUM>), wherein:
the turbo-expander (<NUM>) operates to rotate the turbo-crankshaft (<NUM>) as a flow of exhaust gas from a combustion process passes through the turbo-expander (<NUM>), and
the turbo-compressor (<NUM>) operates to compress the flow of exhaust gas after the exhaust gas passes through the turbo-expander (<NUM>);
an exhaust gas processing system (<NUM>) comprises at least one of a cooling tower (<NUM>), a cooling tower heat exchanger (<NUM>), an absorption chiller (<NUM>), an absorption chiller heat exchanger (<NUM>), a dehumidifier system (<NUM>) and a vapor-compression refrigeration system;
characterised in that the system further comprises:
an exhaust gas heat exchanger (<NUM>) comprising a first flow path (<NUM>) and a second flow path (<NUM>) which operate to exchange heat therebetween, wherein:
the first flow path (<NUM>) operates to receive the flow of exhaust gas from the turbo-expander (<NUM>) prior to the exhaust gas being compressed by the turbo-compressor (<NUM>), and
the second flow path (<NUM>) operates to receive the flow of exhaust gas from the turbo-compressor (<NUM>) after the exhaust gas has been compressed by the turbo-compressor (<NUM>); and
wherein the exhaust gas processing system (<NUM>) receives and cools the flow of exhaust gas after the exhaust gas has passed through the first flow path (<NUM>) of the exhaust gas heat exchanger (<NUM>) and prior to the exhaust gas being compressed by the turbo-compressor (<NUM>).