A combined heat and power system that generates and uses CO2, and a method of operation.

Abstract

A combined heat and power (CHP) system and method of operation are provided. The CHP system comprises an oxygen-air separation device. A combustion chamber has an inlet connected to the oxygen-air separation device. The combustion chamber receives an expanded and heated CO2 working gas for the combustion of a solid fuel and generates a CO2 exhaust gas. The expanded and heated CO2 working gas contains at least a portion of the CO2 exhaust gas. A heat exchanger receives the combustion gas and outputs a cooled CO2 working gas. A turbine is provided having a compression section and an expansion section, the compression section configured to receive and compress the cooled CO2 working gas and direct it toward a heat exchanger. The turbine receives a heated CO2 working gas in the expansion section and expands the heated CO2 working gas. In embodiments, CO2 products may be generated from the system.

Description

Technical Field

[0002]

[0001] Cross - References to Related Applications This application claims the priority and benefit of U.S. Patent Application No. 18 / 203973, titled "Combined Heat and Power System Using And Producing CO2 And Method Of Operation", filed on May 31, 2023, the content of which is incorporated herein by reference.

[0002] The subject matter described herein relates to a combined heat and power system, and more particularly to a heat system that utilizes waste organic resources and converts the waste organic resources into thermal energy used to drive a gas turbine coupled to a heat system for generating electricity, and high - level usable waste heat for both low - temperature heat applications and high - temperature heat applications.

Background Art

[0003] Combined heat and power (CHP) systems have been utilized in many forms for over 100 years. The most common are fossil - fuel - fired systems that use, for example, steam turbines, gas - fired turbines, and internal combustion engines to generate electricity. The waste heat from these systems can be used for a wide range of applications such as heating and cooling, and can also be used to drive a second cycle if the waste heat temperature is high enough. Most of the focus on conventional CHP systems has been on large - scale fossil - fuel - fired systems connected to district heating systems. Over the past 30 years, the focus has shifted to smaller, distributed CHP systems where the generated heat or electricity can be better utilized by end - users. These systems have also been fossil - fuel - fired systems that generally use small gas turbines or reciprocating engines to generate electricity along with usable waste heat. Other systems using an organic Rankine cycle have also been used, but the quality of the waste heat is relatively low, which limits the applications for the use of the generated heat.

[0004] More recently, there has been a desire to focus on using renewable organic waste streams for fuel. Large quantities of biomass and municipal waste have been used in power systems for decades. The ability to utilize a wide variety of organic sources in small-scale CHP systems (e.g., less than 1 MW of electricity) has been challenging for several reasons. Many small-scale organic-to-electricity conversion technologies have been used with varying degrees of success. The production of synthesis gas ("singus") by gasification of organic matter was one method for converting solid fuels into hydrocarbon gases for combustion in conventional power systems. Unfortunately, these systems can be costly, especially when scaled down to smaller power / heat applications. Also, organic raw materials can present specific challenges in application. For example, depending on the gasification method and conversion efficiency, the potential energy available in some organic materials suffers losses that have an economic impact on the cost of electricity and heat. Gasification of mixed organic residues can be particularly problematic for many gasification systems.

[0005] Another approach applicable to small-scale CHP applications was to use the direct combustion of organic matter through a suitable combustor and utilize the heat through a heat exchanger to drive an external heat engine. Conventional external heat systems include the Stirling cycle, steam Rankine, organic Rankine, and supercritical CO2 cycle. In all of these systems, the temperature of the waste heat affects the cycle efficiency. As the waste heat temperature increases, the power efficiency decreases. With the exception of the steam cycle, other thermodynamic cycles typically lose efficiency even when producing hot water at 90°C. However, in the case of the steam cycle, its drawbacks are the complexity and cost associated with high-pressure steam circuits in small-scale applications.

[0006] Another method employed involves using an open Brayton cycle gas turbine and introducing heat indirectly through a heat exchanger. Several systems have been tested where a small turbine is coupled to an organic combustion system. In these systems, ambient air is compressed in the turbine's compressor and then directed to a reheater to heat the compressed air. The compressed air is heated by the organic combustion system. The hot air is then expanded in the turbine to generate work to turn a generator and produce electricity. If the cycle continues, the hot turbine air is used to preheat the combustion air. The hot gas from the turbine exhaust can then be discharged or directed to a further heat exchanger from which usable waste heat can be extracted.

[0007] In some cases, the focus has also been on reducing, capturing, and sequestering CO2 from power plant emissions. There are several methods for extracting CO2 from exhaust gases, including adsorption, membrane, cryogenic, and electrochemical methods. Each of these systems incurs considerable capital costs in addition to the energy consumption required to capture CO2 from exhaust gases.

[0008] Another method to eliminate the need to extract CO2 from exhaust gases is to use an oxygen-fuel ("oxyfuel") combustion system. In this system, oxygen is separated from the air and used to oxidize hydrocarbons to produce CO2 and water. Oxyfuel systems are used in the glass, steel, and ceramics industries to eliminate NOx associated with high-temperature furnaces. Only a few oxyfuel power systems have been developed, particularly the Aram cycle, which uses an oxyfuel burner with gaseous fuel in a supercritical CO2 cycle. Oxyfuel systems have not been introduced for handling solid organic materials such as biomass, plastics, and other organic residues. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, while existing CHP systems are suitable for their intended purposes, there remains a need for improvement, particularly in providing a CHP system having the features described herein. [Means for solving the problem]

[0010] According to one aspect of the present disclosure, a combined heat and power (CHP) system is provided. The CHP system is a combustion system having an oxygen-air separation device, a combustion chamber, and a feeding mechanism configured to feed a solid fuel into the combustion chamber, wherein the combustion chamber has a gas inlet for combustion and a combustion gas exhaust port, the gas inlet being fluid-coupled to the oxygen-air separation device, the combustion chamber is configured to receive an expanded and heated CO2 working gas into the gas inlet for combustion of a solid fuel, and the combustion chamber is configured to generate a CO2 exhaust gas substantially containing CO2 gas, and a first proportional valve fluid-coupled to the gas inlet and configured to control the flow of the heated and expanded CO2 working gas into the gas inlet, wherein the heated and expanded CO2 working gas contains at least a portion of the CO2 exhaust gas, and a first proportional valve operably connected to the combustion chamber and configured to release the hot combustion gas from the combustion chamber A gas turbine comprising: an exhaust plenum configured to receive; a high-temperature heat exchanger operably connected to the exhaust plenum and configured to receive combustion gases from the exhaust plenum and output cooled CO2 working gas, the high-temperature heat exchanger operable to transfer heat from the combustion gases to compressed CO2 working gas; and a gas turbine having a compression section and an expansion section operably connected to a drive shaft, wherein the compression section is configured to receive cooled CO2 working gas at an inlet, compress the cooled CO2 working gas, and direct the compressed CO2 working gas toward the inlet of the high-temperature heat exchanger, and the gas turbine is configured to receive heated CO2 working gas at an inlet to the expansion section in order to expand the heated CO2 working gas and generate work from the heated CO2 working gas.

[0011] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include a mixing plenum fluidly coupled between the combustion chamber and the exhaust plenum, and fluidly coupled to the expansion zone.

[0012] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include a second proportional valve connected between the expansion zone and the mixing plenum.

[0013] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may further include a temperature sensor capable of operating to sense the temperature of the combustion gases at the combustion gas exhaust port.

[0014] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may further include a temperature sensor which is at least one of a thermocouple, an infrared detector, and a semiconductor detector.

[0015] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include a first proportional valve, an oxygen-air separation unit, and a mixing valve fluid-coupled to the gas inlet.

[0016] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include a mixing valve further fluid-coupled to the gas fuel source.

[0017] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include a control valve that is fluidly coupled between the outlet of a high-temperature heat exchanger and the inlet of a gas turbine and configured to extract a portion of the cooled CO2 working gas.

[0018] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include an external process device fluidly coupled to a control valve.

[0019] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include an external process device comprising a filter device configured to output purified CO2 gas.

[0020] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may further include an external process device comprising at least one of a compressor, a compressed gas storage system, a CO2 liquefaction system, a dry ice generator, and a solid carbon conversion process.

[0021] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include an oxygen sensor positioned to measure gas between the exhaust plenum and the high-temperature heat exchanger.

[0022] In addition to or as an alternative to one or more of the features disclosed herein, further embodiments of the CHP system may include a high-temperature particle separator having an inlet and an exhaust port, which is fluid-coupled to a combustion chamber and configured to receive high-temperature combustion gases from the combustion chamber, and further includes an exhaust plenum.

[0023] In addition to, or as an alternative to, one or more of the features disclosed herein, further embodiments of the CHP system may include a high-temperature particle separator comprising at least one cyclone separator, which is operably connected to a hopper for the removal of particulate matter.

[0024] According to another aspect of the present disclosure, a method of operating a combined heat and power (CHP) system is provided. The method includes, during a start-up mode, starting a combustion process in a combustion chamber to generate an exhaust gas consisting substantially of CO2 gas, burning a solid fuel together with an oxygen-fuel gas, adjusting the temperature of the hot combustion gas from the combustion chamber with an expanded and heated CO2 working gas to produce a mixed CO2 combustion gas, transferring thermal energy from the mixed CO2 combustion gas by a heat exchanger to generate a cooled CO2 working gas, compressing the cooled CO2 working gas to generate a compressed CO2 working gas, heating the compressed CO2 working gas with thermal energy to generate a compressed and heated CO2 working gas, and expanding the compressed and heated CO2 working gas to thereby generate work.

[0025] In addition to, or alternatively to, one or more of the features disclosed herein, a further embodiment of the method may include generating an oxygen gas and mixing a fuel gas to generate an oxygen-fuel gas during the start-up mode.

[0026] In addition to, or alternatively to, one or more of the features disclosed herein, a further embodiment of the method may include the fuel being at least one of propane, natural gas, or methane.

[0027] In addition to, or alternatively to, one or more of the features disclosed herein, a further embodiment of the method may include flowing at least a portion of the expanded and heated CO2 working gas to the combustion chamber during the operating mode.

[0028] In addition to, or alternatively to, one or more of the features disclosed herein, a further embodiment of the method may include extracting at least a portion of the cooled CO2 working gas during the operating mode.

[0029] In addition to, or alternatively to, one or more of the features disclosed herein, further embodiments of the method may include that the amount of the extracted cooled CO2 working gas is selected to maintain a substantially constant pressure within the system.

[0030] In addition to, or alternatively to, one or more of the features disclosed herein, further embodiments of the method may include the step of compressing and storing a portion of the cooled CO2 working gas.

[0031] In addition to, or alternatively to, one or more of the features disclosed herein, further embodiments of the method may include the step of filtering a portion of the cooled CO2 working gas.

[0032] In addition to, or alternatively to, one or more of the features disclosed herein, further embodiments of the method may include the step of liquefying a portion of the cooled CO2 working gas.

[0033] In addition to, or alternatively to, one or more of the features disclosed herein, further embodiments of the method may include the step of forming dry ice from a portion of the cooled working gas.

[0034] In addition to, or alternatively to, one or more of the features disclosed herein, further embodiments of the method may include the step of performing a welding operation with a portion of the cooled working gas.

[0035] Other aspects, features, and techniques of the embodiments will become more apparent from the following description in conjunction with the drawings.

[0036] The subject matter to be interpreted as an invention is specifically identified and explicitly claimed in the claims at the end of this specification. The aforementioned and other features and advantages of the present invention will become apparent from the following detailed description in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0037] [Figure 1] This is a schematic block diagram of a combined heat and power system according to an embodiment. [Figure 2] This is a flowchart illustrating a method for controlling a combined heat and power system according to an embodiment. [Modes for carrying out the invention]

[0038] Embodiments of this disclosure relate to a power system having a closed-loop, reheated CO2 Brayton cycle for indirect oxy / solid organic thermal power. In this system, a solid organic fuel is burned at atmospheric pressure in a combustion chamber using high-purity oxygen (93% to 99.5% O2) as the oxidizer. The oxygen is supplied by an air separation unit. The system is a closed-loop that utilizes CO2 as the working fluid and heat transfer fluid for the turbine to transport heat from the combustion chamber to the turbine. The CO2 gas coming from the turbine exhaust is partially routed through the combustion chamber where oxygen and solid fuel are burned. The hot combustion gas, mostly containing CO2, then proceeds to a mixing plenum, where a portion of the cooler turbine exhaust gas is mixed with the hot combustion gas to lower the gas temperature. The mixed gas then passes through a particle separator to remove inorganic solids, and then through a reheater, where heating / thermal energy is transferred to compressed CO2 gas from the compressor. The hot compressor gas is then expanded to generate electricity before returning to the combustion chamber. The combustion gases exiting the reheating unit are at a lower temperature but still possess heat that can be used for thermal purposes, and are therefore cooled before proceeding to the compressor inlet. In some embodiments, exhaust gas cooling can be achieved by a water-cooled heat exchanger to bring it closer to ambient temperature, or by using heat in an absorption cooling cycle to cool the exhaust gas to below 0°C.

[0039] As organic materials are oxidized into CO2 and water, the additional mass will increase the system pressure. A pressure control valve is positioned on the low-pressure side of the system and is used to set a lower or minimum operating pressure for the system. As the pressure increases due to the additional mass, the control valve can release cooled CO2 gas from the system. This maintains a constant average pressure in the system while extracting excess CO2. The gas leaving the system is essentially CO2 with trace amounts of CO, water, and other contaminants, which are therefore removed through subsequent processing to produce pure CO2 for reuse, conversion, or sequestration.

[0040] This system offers numerous advantages, including the use of an oxyfuel combustion system, for oxidizing solid organic matter. This reduces or eliminates nitrogen from the system, provides CO2 as a byproduct used as the working gas, and reduces or eliminates the need to separate CO2 from exhaust gases that are normally mixed with air.

[0041] One advantage of using CO2 as the working gas instead of air is that, at ambient pressure and temperature, CO2 is 60% denser than air. Since there is no change in volume flow through the system, the additional density represents a 60% increase in mass flow, resulting in 60% greater power for the same equipment.

[0042] Another advantage of this system is that the specific heat ratio (Cp / Cv) for CO2 is lower than that for air. This means that for the same pressure ratio, the differential temperature across the compressor and expander is lower for CO2 than for air. This consequently results in a larger differential temperature across the reheating unit and, furthermore, higher thermal-electrical efficiency compared to air for the same high and low temperatures.

[0043] Another advantage of this system is that, by using oxygen, the oxygen / fuel ratio can be controlled independently of turbine speed and power. This allows for more complete combustion over a wider range of operating conditions, including partial load conditions.

[0044] Another advantage is that exhaust emissions are captured by CO2 and condensate. This reduces or eliminates the need for exhaust stacks associated with air-cycle power systems, and further reduces or eliminates the need for requirements to enable emissions into the power system.

[0045] Another advantage of this system is that the product is almost pure CO2 (over 98%), requiring minimal post-processing to produce CO2 that can be used for secondary purposes, such as welding gas, food and beverages, dry ice, liquid CO2, or conversion to many other carbon products.

[0046] The CHP system begins by starting the turbine at a desired lower speed, such as 20% of full speed. The valve from the turbine to the combustion chamber is opened, and the valve from the turbine to the mixture plenum is closed, directing all flow into the combustion chamber. Ignition begins with the gaseous fuel (methane, propane, syngas) being fed into the oxygen fuel burner. Oxygen gas is supplied by the air separation unit. The burner transfers heat to the flowing gas to raise the system temperature. As the combustion temperature rises, the turbine speed is increased to keep the differential temperature across the first heat exchanger within limits. When the temperature in the combustion chamber reaches a desired temperature, such as 600°C, solid fuel is fed into the combustion chamber, and the gaseous fuel is stopped. Oxygen continues to be supplied in proportion to the solid fuel to maintain the desired oxygen / fuel ratio for stoichiometric combustion. The fuel-oxygen ratio is increased to raise the system temperature. When the combustion chamber temperature reaches a desired operating temperature, such as 800°C, the valve to the mixture plenum begins to open. A temperature sensor located at the inlet of the first heat exchanger and connected to the plenum valve controls the temperature of the gas exiting the mixture plenum. The combustion chamber temperature continues to rise until it reaches a desired temperature, such as over 1000°C, to provide the desired level of combustion. A temperature sensor located at the outlet of the combustion chamber and connected to the combustion chamber valve controls the combustion chamber temperature. As the temperature rises to the operating temperature, the turbine speed is increased to the maximum speed and power. Once the operating temperature is reached, the power is controlled by controlling the torque of the generator and by regulating the fuel delivery and oxygen rate to the combustion chamber.

[0047] In further embodiments, one or more embodiments are provided of a combined heat and power system that utilizes waste organic resources and converts them into thermal energy used to drive a gas turbine connected to a thermal system to generate electricity, and high levels of usable waste heat for both low-temperature and high-temperature applications.

[0048] Referring to Figure 1, there is a combined heat and power (CHP) system 100 according to an embodiment. The CHP system 100 utilizes a combustion system 21, a closed-cycle Brighton gas turbine 22, a high-temperature cyclone particle separator 42, a high-temperature heat exchanger 23 for transferring the heat generated in the combustion system 21 to the turbine 22, and low-temperature heat exchangers 24 and 25.

[0049] Indirect thermal power systems typically utilize at least one heat exchanger to transfer heat from the combustion process to the engine's working gases. Depending on the type of engine cycle, heat transfer will occur at different temperatures. For cycles such as organic Rankine, the temperature delivered to the engine rarely exceeds 500°C, and more typically below 250°C. The advantage of using an ORC is that it allows for the utilization of lower temperature heat, and subsequently, lower-cost heat exchangers. The disadvantages are lower efficiency, higher cost, and the low-temperature waste heat, typically below 90°C, that is excluded from the cycle and is not readily available elsewhere.

[0050] Therefore, it is often desirable to use higher-temperature cycles, such as the open Brighton cycle, to more directly and efficiently utilize the high temperatures available from the combustion system 21. Current Brighton turbine engines are designed to utilize heat at approximately 950°C. The advantages of higher-temperature cycles are higher efficiency, lower cost, and the removal of high-temperature waste heat from the cycle, which can typically reach as high as 600°C.

[0051] In embodiments, the combustion system 21 further comprises a combustion chamber or housing 28 for burning organic fuel to generate heat, but is not limited to these. Biomass fuels, i.e., organic materials, include, for example, woody fuels such as wood chips and pampas grass, animal waste, i.e., fertilizers, non-halogenated plastics, or general waste (MSW). The combustion chamber 28 also comprises an opening, valve, or port 29 for supplying fuel to the combustion chamber 28. In embodiments, an air-oxygen separator 32 is provided which extracts oxygen from the air and transfers the oxygen gas to an oxygen-fuel burner 31, which accepts a gaseous fuel 33 (e.g., propane, natural gas, methane, etc.) (during the start-up mode of operation) to generate a combustion gas and ignites or burns the oxygen-fuel mixture. This combustion gas is mixed with a working fluid / gas from a conduit 39 and transferred to the combustion chamber 28 via a port 34. As described in more detail herein, the gaseous fuel 33 is used during the start-up mode of operation and then stopped when predetermined operating conditions are met. The temperature of the combustion gas from the oxygen-fuel burner 31 is sufficient to initiate combustion of the biomass in the combustion chamber 28. In at least some embodiments herein, oxygen gas continues to flow into the combustion chamber 28 both at the start and when predetermined operating conditions are met in order to maintain combustion in the combustion chamber without the addition of fuel 33. In some embodiments, the flow of O2 gas is regulated by an air-oxygen separator 32 during steady-state operation. In embodiments, port 34 may also be configured to deliver CO2 gas from the turbine 22 via a proportional valve 35, thereby measuring the combustion gas from the turbine 22.

[0052] The combustion system 21 includes a valve 29 for measuring the mass of solid fuel directed towards the combustion chamber 28, a temperature sensor such as a thermocouple 41 used to measure the combustion exhaust temperature, and a control device 90 for receiving various sensor inputs such as temperature, valve position, and speed, as well as for controlling various valves and electric motors in the system 100.

[0053] As discussed herein, it should be understood that the output from the combustion chamber 28 consists mostly of CO2 (90%–98% CO2), CO, N2, particulate matter, and water vapor. The combustion gases from the combustion chamber flow through a conduit to a mixing plenum 40. The mixing plenum 40 also includes a port 65 that receives the expanded gas from the turbine 22 via a proportional valve 38. The mixing plenum 40 flows the heated combustion gas / working gas to a downstream conduit equipped with a temperature sensor or thermocouple 44 that measures the gas flow and provides a feedback signal to the control unit 90. The hot mixed gas is transferred through a port 43 to a particle separator 42.

[0054] In the embodiment, the particle separator 42 further comprises one or more cyclones 45, a detachment hopper 48 for particle recovery, a mechanical auger 46 for removing particles from the hopper 48, and a motor 47 for driving the auger 46. The particle separator 42 is designed to operate at a maximum heat exchanger temperature of about 850°C and is constructed from materials capable of operating at such temperatures and is also designed to be resistant to the effects of combustion gas abrasion and corrosion. In the embodiment, the particle separator 42 is constructed from a nickel alloy metal that provides thermal shock resistance, abrasion resistance, and high temperature strength characteristics. The cyclone particle separator may be a reverse flow, forward flow, or other type of cyclone configuration. The cyclone particle separator 42 also comprises an exhaust plenum 48 connected to a conduit 51 containing an oxygen sensor 50 that provides a feedback signal to a control device 90.

[0055] The CHP system 100 also includes a high-temperature heat exchanger 23, which has a first port 52 for directing high-temperature combustion gases into the heat exchanger 23, an outlet port for directing low-temperature combustion gases out of the heat exchanger 23, an inlet port 60 for directing low-temperature compressed air into the heat exchanger 23, and a port 61 for directing high-temperature air from the heat exchanger 23 to the expansion turbine 27. The high-temperature heat exchanger 23 is configured to operate at temperatures as high as approximately 1000°C. Heat exchangers capable of operating at the high temperatures required for this application typically operate near the structural limits of the metal used, usually made from stainless steel or nickel alloy. Therefore, careful and precise control of the combustion gas temperature ensures that the desired temperature limits of the material of the high-temperature heat exchanger 23 are not exceeded. There is also control of the differential temperature between the exhaust gas entering the high-temperature heat exchanger 23 and the working gas leaving the heat exchanger 23. A smaller differential temperature results in a smaller maximum operating temperature for the heat exchanger. A smaller differential temperature reduces stress in the high-temperature heat exchanger 23, extending its lifespan. For example, given a desired turbine inlet temperature of 900°C, the combustion gas will be delivered at 960°C for the given effect.

[0056] In this embodiment, a single-counterflow heat exchanger is used to improve the thermoelectric efficiency of the CHP system 100. It is understood that other heat exchanger configurations are possible. In this embodiment, a single-counterflow microchannel plate or tubular heat exchanger made of stainless steel or nickel alloy is used, but is not limited to, other types may be available, including tube-and-shell, microtube, microchannel, and plate types. In this embodiment, the high-temperature heat exchanger may be constructed from ceramic or nickel alloy steel. Advantageously, ceramic heat exchangers can operate at temperatures above 1100°C, while conventional metal heat exchangers typically cannot exceed 900°C. Although ceramic heat exchangers have several advantages, in this embodiment, a metal heat exchanger is used. Controlling the temperature of the combustion gas entering the high-temperature heat exchanger 23 reduces costs in two ways. First, by strictly controlling the temperature of the combustion gas entering the high-temperature heat exchanger 23, it is possible to use a metal heat exchanger instead of a considerably more expensive ceramic heat exchanger. Ceramic heat exchangers can be up to 200% more expensive than nickel alloys. In some cases, this allows for the use of stainless steel instead of the more costly nickel alloys. A second cost saving lies in the extended lifespan of the heat exchanger, which reduces maintenance costs over time. Power generation equipment is typically expected to have a service life of 20 years. Reducing thermal stress through well-controlled combustion gas temperatures ensures longer operation of the heat exchanger, achieving a 25% reduction in maintenance costs over the lifespan of the power plant.

[0057] In the embodiment, a gas at a lower temperature exits the high-temperature heat exchanger 23 and passes through one or more low-temperature heat exchangers 24, 25 to further reduce the temperature of the CO2 gas for use in auxiliary operations (not shown). In the embodiment, the first low-temperature heat exchanger 24 receives the CO2 gas through port 53 at a temperature of about 250°C and exits through output port 54 at a temperature of about 100°C. In the embodiment, the second low-temperature heat exchanger receives the CO2 gas through port 55 and further extracts thermal energy from the CO2 gas. In the embodiment, the CO2 gas exits the second low-temperature heat exchanger at a temperature from 0°C to near ambient temperature. Heat exchanger 25 is configured to remove condensate from the working gas. In the embodiment, heat exchanger 24 functions as a heat source for an absorption chiller, and heat exchanger 25 is a low-temperature heat exchanger for transferring unusable heat from the working fluid / gas.

[0058] The CHP system 100 is typically operated as a closed-loop system, which should be understood to mean that the generated CO2 gas is reused or recycled within the system. It should be further understood that by adding biomass fuel and oxygen gas to the combustion chamber, the additional mass will increase the pressure within the CHP system 100. In embodiments, a control valve 57 receives a low-temperature, low-pressure CO2 gas flow from a second low-temperature heat exchanger 25. The control valve 57 is configured to maintain a substantially constant pressure within the system 100 by selectively diverting a portion of the CO2 gas flow to an external process 64. In embodiments, the external process 64 receives the CO2 gas flow, which is substantially CO2 with trace amounts of water and other contaminants for further processing. In one embodiment, the gas flow is filtered to remove water and contaminants to a desired level. The substantially pure CO2 thereafter can be reused, converted, or sequestered. In the embodiment, the CO2 gas is converted, for example, into a welding gas, used in food or beverage processes, converted into dry ice, or liquefied to generate liquid CO2.

[0059] The remaining low-temperature CO2 gas flow is transferred via conduit 58 to a closed-cycle Brighton gas turbine 22. In embodiments, the closed-cycle Brighton gas turbine system 22 further includes a turbine compressor 26 for compressing the low-temperature CO2 gas flow from conduit 58, and a fluid connection 59 from the turbine compressor outlet to the heat exchanger inlet port 60, which carries the compressed CO2 gas to a high-temperature heat exchanger 23. The gas turbine system 22 also includes a fluid connection 62 from the outlet port 61 of the high-temperature heat exchanger 23 to the inlet of the expansion turbine 27. The turbine expander 27 expands the CO2 working gas to generate usable work, such as turning a generator to generate electricity. The turbine system 22 also includes a fluid connection from the outlet of the expansion turbine 27, which is fluid-coupled to proportional valves 35, 38. In embodiments, the turbine system may also include a generator connected to the turbine shaft to generate power.

[0060] Referring again to Figure 2, with continued reference to Figure 1, an embodiment of process 200 for controlling the CHP system 100 is shown. Method 200 is started in block 205 by starting the operation of the turbine 22, turning the air-oxygen separator 32, and feeding fuel 33 into the burner 31. The oxygen-fuel mixture is burned / combusted and mixed with the working fluid from the turbine 22 (through the conduit 39) and sent to the combustion chamber 28. In the embodiment, the oxygen-fuel combustion gas mixture is preheated before being injected into the combustion chamber 28. When the combustion chamber 28 is heated to a selected temperature, a solid fuel (e.g., biomass) is introduced through valve 29 and burned. In the embodiment, the temperature at which the fuel is introduced is selected to be 600°C, but other temperatures may be used.

[0061] As the combustion process continues, the temperature of the combustion gases increases to the operating temperature of the combustion system 21. A proportional valve 35 controls the mass flow of the working gases, and a burner valve 31 controls the mass flow of oxygen entering the combustion port 34 in the combustion chamber 28. The proportional valves 35, 38 can be any automatically controlled valves, including butterfly, gate, ball, flapper, or other mechanical systems. The proportional valve 35 may be driven by a servo motor 36 connected to the valve 35. The proportional valve 35 can be driven by the DC servo motor 36 hydraulically, pneumatically, or by other electromechanical position systems. The servo motor is connected to a control device 90 and driven by signals from the control device 90.

[0062] Combustion systems utilizing organic materials generally control the air / fuel ratio using an oxygen sensor or lambda sensor 50 that provides a feedback signal to a control device 90. The control device 90 includes one or more processing units that respond to executable commands to perform a control method to alter the fuel (through valve 29) and / or oxygen (from air-oxygen separator 32) supplied to the combustion chamber 28. In the CHP system 100, the oxygen sensor 50 may be used to ensure a positive oxygen / fuel ratio during the start-up mode and during normal operation with organic materials.

[0063] One way to control the heat generation rate in the CHP combustion system 100 is to utilize a proportional valve 35 that can vary the combustion gas flow over a range such as 0% to 100%. In operation when burning organic materials with a consistent moisture content, the proportional valve 35 supplies a sufficient mass flow to absorb heat from the burned organic material in order to meet the required heat requirements. When all conditions are constant, there is little need to control the air / fuel except when there are variations in requirements.

[0064] In the embodiment, the target operating temperature for the combustion process is above approximately 1000°C, depending on the combustion chamber and fuel type used. It is understood that other combustion operating temperatures are possible. It is understood that the desired operating temperature for the combustion process may be selected based on several factors. Generally, higher temperatures are desirable for complete combustion of the fuel with less particulate matter emission. Conversely, lower temperatures may be desirable for downstream components such as heat exchangers.

[0065] The combustion gas temperature is measured at the outlet by a temperature sensor 41, such as a thermocouple, IR sensor, or semiconductor sensor, and is used to control both the fuel delivery rate to the combustion chamber 28 and the high-temperature gas directed to the downstream process. In the embodiment, the control device 90 has a setpoint temperature, which is defined as the average combustion temperature. In the embodiment, the control device 90 uses time-averaged temperature measurement to control the valve 29 in order to control the fuel delivery rate. By using time-averaged temperature measurement to control the valve 29, the valve 29 can maintain a more constant flow instead of responding to fluctuations in the output temperature of the combustion gas. The gas temperature leaving the combustion chamber 28 can reach 1050°C, which may exceed the maximum temperature for the heat exchanger. However, high temperatures are desirable to achieve complete combustion and to eliminate unburned hydrocarbon emissions.

[0066] As the CO2 gas exits the combustion chamber 28, method 200 proceeds to block 210, where the gas flow enters a part of a system that regulates the temperature of the working fluid to the high-temperature heat exchanger 23. In an embodiment, the high-temperature working fluid / gas from the turbine 27 is directed through conduit 39 and enters a mixing plenum 40. The mixing plenum 40 mixes the high-temperature combustion gas from the combustion chamber 28 with the relatively lower-temperature working fluid / gas from the turbine 27 to control the temperature of the working fluid / gas proceeding to the heat exchanger 23. In an embodiment, the gas temperature to the heat exchanger 23 depends on the threshold working temperature rating of the heat exchanger. The mixing plenum 40 offers an advantage in that it allows control of the temperature of the combustion chamber 28 independently of the temperature of the heat exchanger 23.

[0067] In this embodiment, a temperature sensor 44 is used to sense the temperature of the combustion gas entering the mixed plenum 40 and to provide a feedback signal to a control device 90 that acts on a control valve 38. The control algorithm will open or close the valve 38 in response to any deviation from the setpoint temperature. A PID control loop is used to adjust the valve position in response to the temperature sensor 44 in order to adjust the position and sensitivity of the valve 38. In this embodiment, the control device 90 responds to any deviation from the setpoint temperature of the heat exchanger 23 by proportional decay of the rate change signal in the proportional valve 38. In this embodiment, the temperature of the combustion gas leaving the plenum 40 is adjusted to the maximum temperature capacity of the high-temperature heat exchanger 23. In this embodiment, the temperature of the combustion gas is adjusted to approximately 900°C. In another embodiment, the temperature of the combustion gas is adjusted to 800°C. In this embodiment, the temperature is adjusted to a tolerance of +100°C. In another embodiment, the tolerance is +50°C. In yet another embodiment, the temperature is maintained within a range of +10°C.

[0068] As the CO2 gas exits the mixed plenum 40, method 200 proceeds to block 215, where the gas flow enters a particle separator or filter 42 to separate particulate matter from the combustion gas. In this embodiment, a high-temperature cyclone particle separator is used, but other forms of particle separators and filters may be utilized. In this embodiment, the high-temperature cyclone particle separator is configured to ensure that 99% of particles larger than 10 microns are removed from the high-temperature combustion gas. As the gas passes through the cyclone 45, the particles are accelerated toward the outer shell and travel down the length of the cyclone. At the bottom of the cyclone 45, the particles fall from suspension to a detachment hopper 48. In this embodiment, the particles collected in the detachment hopper 48 are removed by a mechanical auger 46 and motor 47. The auger motor 47 can be operated intermittently or continuously, depending on the quality of the inorganic material in the solid fuel and the size of the auger 46 and hopper 48. Therefore, the gas continues to move upwards in the center of cyclone 45 and exits upwards into exhaust plenum 48.

[0069] Control of the CHP combustion system 100 and the secondary air valve 38 begins with the electrical load in the turbine 22 and load / generator (if present). The turbine speed will change in response to the electrical load, which will alter the working gas flow through the expansion turbine 27, thereby heating the working gas in the high-temperature heat exchanger 23. A high threshold turbine inlet temperature is limited by the heat exchanger temperature limit / rating and efficiency. In the embodiment, a temperature sensor 44 senses the working gas temperature exiting the mixed plenum 40. This temperature may be a constant setpoint temperature. To maintain the setpoint temperature, the combustion gas flow to the high-temperature heat exchanger 23 may be adjusted based on the change in temperature detected by the temperature sensor 44 to deliver a precise amount of energy. This is achieved by the control device 90 diverting the fuel through the valve 29 to the combustion chamber 28 to deliver the desired energy.

[0070] A temperature sensor 41 may be used to control the temperature of the combustion gases leaving the combustion chamber. The temperature sensor 41 measures the instantaneous temperature of the gas and transmits it to the control device 90. The time-averaged value is used to compare with a setpoint value in the combustion chamber 28 to control the amount of fuel and oxygen to maintain a desired setpoint temperature. The instantaneous value may be compared with a setpoint value to determine the magnitude of the deviation from the setpoint value. When the temperature sensor 41 detects a deviation from the setpoint temperature, the control device 90 predicts the exhaust gases reaching the plenum 40 and begins to adjust the valve 35. The oxygen sensor 50 provides a feedback signal to the control device 90 to ensure a positive oxygen / fuel ratio during the start-up mode and normal / continuous / steady-state operation. In embodiments, the control device 90 adjusts at least one of the following in response to the signal from the oxygen sensor 50: the amount of oxygen gas from the oxygen-air separator 32, the amount of heated and expanded CO2 working gas from the proportional valve 35, or the amount of solid fuel from the valve 29.

[0071] In the starting mode, proportional valve 35 is fully open and proportional valve 38 is fully closed until the temperature measured by a temperature sensor 41, which measures the temperature of the combustion gases leaving the combustion chamber 28, exceeds a desired inlet setpoint temperature for the heat exchanger 23. As proportional valve 38 opens, heated gas from the expansion turbine 27 in the piping 39 is mixed with the combustion gas in the mixing plenum 40 to maintain and regulate the high-temperature combustion gases directed towards the high-temperature heat exchanger 23 to a substantially constant temperature within a desired tolerance. Proportional valve 38 controls the mass flow of high-temperature working gases entering the secondary port 65 before the particle separator 42. Proportional valve 38 can be any automatically controlled valve, including butterfly, gate, ball, flapper, or other mechanical systems. A servo motor 37 is connected to a control device 90 and driven by signals from the control device 90.

[0072] Method 200 proceeds to block 225, where, as the high-temperature combustion gas passes through the high-temperature heat exchanger 23, heat is transferred from the combustion gas to the CO2 working gas of the turbine 22. In embodiments, after the heat has been transferred to the working gas, the combustion gas may be used for secondary purposes to improve the efficiency and effectiveness of the CHP system 100. In embodiments, the combustion exhaust gas temperature exiting the high-temperature heat exchanger 23 can be as high as approximately 300°C. However, it is understood that the temperature of the exhaust gas exiting the high-temperature heat exchanger 23 depends on the heat exchanger efficiency. Higher heat exchanger efficiency will result in lower exhaust temperatures. The temperature of the exhaust gas entering the high-temperature heat exchanger 23 also has an effect. In applications where the exhaust gas entering the high-temperature heat exchanger 23 is regulated to a lower temperature, for example 800°C, the temperature exiting the heat exchanger 23 will be lower.

[0073] A secondary purpose of using the combustion gas is to provide usable high-temperature heat. In embodiments, the combustion gas can pass through a second low-temperature heat exchanger 24 and a third low-temperature heat exchanger 25 used to prevent further heat from the combustion gas. Examples of lower-temperature applications that may be utilized from the heat exchanger 24 include processes involving power generation in a second-cycle ORC system, for generating further work or electricity, high-temperature water, absorption chilling, low-temperature drying applications such as sludge drying, thermal water purification, and heating and cooling of space. In embodiments, the heat exchanger 24 is used in an absorption cooling system (e.g., an absorption chiller) to provide a low-temperature heat sink to the heat exchanger 25. The heat exchanger 25 reduces the CO2 gas temperature to about 0°C, which consequently results in the condensation of water from the gas, which can be removed in the heat exchanger 25. The further cooled combustion gas exits the low-temperature heat exchanger 25.

[0074] As discussed herein, in embodiments, in block 227, the cooled CO2 gas leaving the heat exchanger 25 is regulated by valve 57, and a portion of the cooled CO2 combustion gas is withdrawn from system 100 to maintain a desired pressure level in the system for the addition of fuel via valve 29 and oxygen from air-oxygen separator 32. This extraction of CO2 can be used for various secondary end uses 64 as described herein. The remaining cooled CO2 gas is sent to turbine 22 via conduit 58.

[0075] The turbine 22 can be started by a starter motor / generator 63. In one embodiment, the turbine 22 is driven by a motor, and CO2 gas is sent through conduit 59 to a high-temperature heat exchanger 23, where the CO2 working gas is heated and expands toward the expansion turbine 27 (block 235). As the shaft rotates and the gas flows through the compressor turbine 26, the CO2 gas begins to flow, and the compressed CO2 expands to further accelerate the flow, and the system's rotation increases with increasing heat over time. Motor / generator speed control can be performed by torque control. When the turbine 22 starts to rotate, the heated expansion turbine exhaust gas is available in piping 39 to supply secondary gas to valves 38 and port 65, and to supply secondary gas to primary combustion gas through valve 35 for combustion system port 34 (block 245).

[0076] As the turbine speed increases, the primary combustion gases supplied to the combustion chamber 28 also increase. In one embodiment, during the start-up mode, the primary combustion gases are gaseous fuels 33 (e.g., propane, natural gas, methane) combined with oxygen from the air-oxygen separator 32. A thermocouple 41 senses changes in the combustion exhaust gas temperature and sends a signal to the control unit 90 to change the rate of solid fuel delivery by changing the speed of the rotary valve 29, and to change the oxygen rate from the air separation unit 32 to adjust the combustion system and continue the cycle. In another embodiment, a proportional valve 35 is controlled to maintain the gas flow permitted by the combustion chamber piping 39 and to accept heat from combustion. Control of the primary combustion gases is performed by the proportional valve 35 when the fuel delivery rate increases / decreases to meet load requirements. During the operating mode / state, the gaseous fuels 33 are stopped / interrupted.

[0077] When system 100 reaches thermal equilibrium, the proportional valve 35 is set to allow sufficient gas flow to maintain a desired combustion temperature. The fuel system responds to the load applied to the turbine 22. In this embodiment, when power is required, the turbine 22 draws heat from the high-temperature heat exchanger 23. Temperature sensors 41 and 44 in the piping sense changes in the temperature of the high-temperature gas supplied to the heat exchanger and determine whether to burn more or less fuel depending on the power demand. Accordingly, the control device 90 commands the rotary valve 29 to increase or decrease its speed in order to allow / maintain sufficient fuel energy to provide the heat required to maintain the setpoint temperature sensed in the conduit 51. In response to changes in fuel speed, the lambda sensor 50 sends a signal to the control device 90 to maintain the desired oxygen demand from the air separation unit 32 in order to achieve complete combustion. The proportional valve 35 is controlled by the control device 90 using several signal inputs and proportional-integral-derivative (PID) positioning control algorithms and signals. The temperature sensor 41 measures the outlet temperature of the combustion chamber 28, and this outlet temperature is maintained at a desired combustion temperature of approximately 1000°C in order to achieve a desired level of combustion.

[0078] Incidentally, the term “exemplary” is used herein to mean “provided as an example, example, or case.” Any embodiment or design described herein as “exemplary” is not necessarily designed to be preferable or advantageous to any other embodiment or design. The terms “at least one” and “one or more” are understood to include any integer one or more, i.e., 1, 2, 3, 4, etc. The term “more” is understood to include any integer two or more, i.e., 2, 3, 4, 5, etc. The term “connection” may include indirect “connections” and direct “connections.”

[0079] Various features of this disclosure are presented as illustrated and described herein. Different embodiments may have the same or similar features, and therefore the same or similar features may be denoted by the same reference numeral, but different first numbers may precede the figure in which the feature is shown. For example, element "a" shown in Figure X may be denoted "Xa", and a similar feature in Figure Z may be denoted "Za". Similar reference numerals may be used in an inclusive sense, but different embodiments are described so as to be understood by those skilled in the art, whether explicitly stated or understood by those skilled in the art, and different features may include modifications, substitutions, improvements, etc.

[0080] The term “approximately” is intended to include the degree of error associated with the measurement of a specific quantity, based on the equipment available at the time of filing this application. For example, “approximately” could include a range of ±8%, 5%, or 2% of a given value.

[0081] The terminology used herein is for the sole purpose of describing specific embodiments and is not intended to be limiting. Although the present invention is described in detail in relation to only a limited number of embodiments, it should be readily apparent that the invention is not limited to such embodiments. There are several variations, alternatives, substitutes, or equivalent configurations that are not described herein but are consistent with the spirit and scope of the claims. Furthermore, although various embodiments are described, it should be understood that aspects of the present invention may include only some of the embodiments described herein. Accordingly, embodiments should not be understood as being limited by the foregoing description, but only by the scope of the appended claims. [Explanation of symbols]

[0082] 21 Combustion System 22. Closed-cycle Brighton gas turbine system 23 High temperature heat exchanger 24, 25 Low temperature heat exchanger 26 Turbine Compressor 27. Expansion turbine, turbine expander 28 Combustion chamber, housing 29 Valves, ports, rotary valves 31. Oxygen-fuel burner, burner valve 32. Air-oxygen separator, air separation unit 33. Gaseous fuels 34 Combustion Ports 35 Proportional valve 37 Servo motor 38. Proportional valves, control valves, secondary air valves 39 Conduits, piping 40 Mixed Plenum 41 Temperature sensor 42 High-temperature cyclone particle separator, filter 43 Ports 44 Temperature sensors, thermocouples 45 Cyclone 46 Ogre 47 Motor 48 Detachable hopper, exhaust plenum 50 Oxygen sensors, lambda sensors 51 Conduit 52 First port 53 ports 54 output ports 55 ports 57 Control valve 58 Conduit 59 Fluid connections, conduits 60 Heat exchanger inlet ports 61 Exit Ports 62 Fluid connection section 64. External processes, secondary end use 65 Secondary Ports 90 Control device 100 Combined Heat and Power (CHP) Systems

Claims

1. Oxygen-air separation device, A combustion system comprising a combustion chamber and a feeding mechanism configured to feed solid fuel into the combustion chamber, wherein the combustion chamber has a gas inlet for combustion and a combustion gas exhaust port, the gas inlet is fluidly connected to an oxygen-air separation device, the combustion chamber is configured to receive an expanded and heated CO2 working gas into the gas inlet for the combustion of the solid fuel, and the combustion chamber is configured to generate a CO2 exhaust gas substantially containing CO2 gas. A first proportional valve is fluid-connected to the gas inlet and configured to control the flow of the expanded and heated CO2 working gas to the gas inlet, wherein the expanded and heated CO2 working gas includes at least a portion of the CO2 exhaust gas. An exhaust plenum operably connected to the combustion chamber and configured to receive high-temperature combustion gases from the combustion chamber, A high-temperature heat exchanger operably connected to the exhaust plenum, configured to receive combustion gas from the exhaust plenum and output cooled CO2 working gas, wherein the high-temperature heat exchanger is operable to transfer heat from the combustion gas to compressed CO2 working gas, A gas turbine having a compression section and an expansion section operably connected to a drive shaft, wherein the compression section is configured to receive the cooled CO2 working gas at an inlet, compress the cooled CO2 working gas, and direct the compressed CO2 working gas toward the inlet of a high-temperature heat exchanger, and the gas turbine is configured to receive the heated CO2 working gas at an inlet to the expansion section in order to expand the heated CO2 working gas and generate work from the heated CO2 working gas, A combined heat and power (CHP) system equipped with [the following features].

2. The CHP system according to claim 1, further comprising a mixing plenum that is fluidly connected between the combustion chamber and the exhaust plenum and fluidly connected to the expansion region.

3. The CHP system according to claim 1, further comprising a second proportional valve connected between the expansion area and the mixing plenum.

4. The CHP system according to claim 1, further comprising a temperature sensor in the combustion gas exhaust port that is capable of sensing the temperature of the combustion gas.

5. The CHP system according to claim 4, wherein the temperature sensor is at least one of a thermocouple, an infrared detector, and a semiconductor detector.

6. The CHP system according to claim 1, further comprising the first proportional valve, the oxygen-air separation unit, and a mixing valve fluidly connected to the gas inlet.

7. The CHP system according to claim 6, wherein the mixing valve is further fluid-connected to a gas fuel source.

8. The CHP system according to claim 1, further comprising a control valve configured to fluidly connect the outlet of the high-temperature heat exchanger and the inlet of the gas turbine, and to extract a portion of the cooled CO2 working gas.

9. The CHP system according to claim 8, further comprising an external process device fluidly connected to the control valve.

10. The CHP system according to claim 9, wherein the external process device includes a filter device configured to output purified CO2 gas.

11. The CHP system according to claim 10, wherein the external process device further comprises at least one of a compressor, a compressed gas storage system, a CO2 liquefaction system, a dry ice generator, and a solid carbon conversion process.

12. The CHP system according to claim 1, further comprising an oxygen sensor positioned to measure gas between the exhaust plenum and the high-temperature heat exchanger.

13. A CHP system according to claim 1, further comprising a high-temperature particle separator having an inlet and an exhaust port, which is fluidly connected to the combustion chamber and configured to receive high-temperature combustion gas from the combustion chamber, and further including the exhaust plenum.

14. The CHP system according to claim 13, wherein the high-temperature particle separator comprises at least one cyclone separator, the cyclone separator being operably connected to a hopper for the removal of particulate matter.

15. A method for operating a combined heat and power (CHP) system, During the start-up mode, the combustion process is initiated in the combustion chamber to generate exhaust gas consisting substantially of CO2 gas, and solid fuel is burned together with oxygen-fuel gas. In order to generate a mixed CO2 combustion gas, the step of adjusting the temperature of the high-temperature combustion gas from the combustion chamber with an expanded and heated CO2 working gas, The steps include: transferring thermal energy from the mixed CO2 combustion gas using a heat exchanger to generate cooled CO2 working gas; To generate compressed CO2 working gas, the process involves compressing the cooled CO2 working gas, To generate a compressed and heated CO2 working gas, the process involves heating the compressed CO2 working gas with the thermal energy, The steps include: expanding the compressed and heated CO2 working gas to generate work; Methods that include...

16. The method according to claim 15, further comprising the steps of generating oxygen gas during the starting mode and mixing fuel gas to generate the oxygen-fuel gas.

17. The method according to claim 16, wherein the fuel comprises at least one of propane, natural gas, or methane.

18. The method according to claim 15, further comprising the step of flowing at least a portion of the expanded and heated CO2 working gas into the combustion chamber during the operating mode.

19. The method according to claim 18, further comprising the step of extracting at least a portion of the cooled CO2 working gas during the operating mode.

20. The method according to claim 19, wherein the amount of CO2 working gas extracted and cooled is selected to maintain a substantially constant pressure within the system.

21. The method according to claim 19, further comprising the step of compressing and storing the portion of the cooled CO2 working gas.

22. The method according to claim 19, further comprising the step of filtering the portion of the cooled CO2 working gas.

23. The method according to claim 19, further comprising the step of liquefying the portion of the cooled CO2 working gas.

24. The method according to claim 19, further comprising the step of forming dry ice from the portion of the cooled working gas.

25. The method according to claim 19, further comprising the step of performing a welding operation with the portion of the cooled working gas.

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