WO2026062327A1 - Heat engine - Google Patents

Abstract

According to an example aspect of the present invention, there is provided a heat engine (1) comprising a housing (2) comprising a water inlet (3) and a gas inlet (4) in an upper region of the housing (2), and a water outlet (5) and a gas outlet (6) in a lower region of the housing (2), a plurality of alternating water channels (7) and adsorbate gas channels (8) within the housing (2) or adsorbate gas channels (8) within a water compartment of the housing (2), wherein the heat engine (1) comprises nanoporous material (9) as an adsorbent within each of the gas channels (8).

Description

HEAT ENGINE

FIELD

[0001] The present invention relates to a heat engine and a method of manufacturing a heat engine. In particular, certain embodiments of the present invention relate to low- temperature heat engines using rapid thermal swing adsorption of CO2 onto activated carbon. Certain embodiments of the present invention relate to heat engines operating with alternative energy sources, especially to engines operating with waste heat from various sources, like industrial waste heat. The heat engine operates on the principle of thermal swing adsorption. The same principle could be applied to operate an air compressor. More specially, an engine operating with waste heat may be a compressor.

BACKGROUND

[0002] According to the World Energy Outlook, humans consumed 442 EJ (total final energy consumption) in 2022 to power modem life and development. Over one third of this energy, 167 EJ, was used for the industrial sector. It is generally estimated that 20- 50 % of industrial energy consumption is ultimately rejected as waste heat. To reduce the environmental impact of this generation, use and rejection of energy, two general options have been identified: derive the energy from renewable sources, or reduce the amount of energy required for the industrial sector. Reducing industrial energy consumption is subdivided into three routes: reduce total activity, improve energy management, recover and use waste energy.

[0003] From the 3P Perspective, waste heat is generated at the Plant, Process and Product levels. To reduce costs and losses, it is ideal to reuse waste heat in the same process that generated it, or in the nearby area.

[0004] The heat recovery rate for an industry depends on the process and waste heat temperatures; however, for most industries 10-20 % of the input energy could be effectively re-used. Most industries have a waste heat stream in the form of exhaust gasses or cooling fluids: aluminum factories, distilleries and sugar cane plants have waste heat streams less than 100 °C; CHP plants, steam turbines, breweries, and factories that produce cement, ceramics, lime, or chemicals have waste heat streams at around 150 °C; ammonia, glass, and mineral processing plants have heat streams closer to 500 °C; steel plants can have waste heat potential above 500 °C. These streams are typically released to the environment as filtered exhaust gases or hot water. In addition to issues around the efficient use of resources, these heat streams can also cause local anthropogenic heating that can influence wildlife and even weather patterns. Technologies that effectively reuse waste heat can simultaneously reduce plant energy demand and anthropogenic heating.

[0005] Documents US 6630012 B2 and US 6974496 B2 (Battelle’s thermal swing adsorption family) disclose compact adHEX configurations and methods for rapid temperature swings and thermally-enhanced pressure swing adsorption by bringing heatexchange surfaces close to adsorbent media and selectively heating portions of the bed to accelerate regeneration. These patents address rapid cycling for separation/regeneration. They emphasize adHEX design and selective heating/coating approaches.

[0006] Classical PSA/TSA patents (e.g., PSA hydrogen purification families such as US6340382B1 and earlier PSA art) teach multi-bed pressure/temperature swing sequences and optimized adsorbent layering for gas purification at elevated pressures. However those systems are optimized for purity and recovery, not for harvesting mechanical work from rapid TSA cycles. Their bulk bed geometries and valve sequencing typically produce longer cycle times and higher thermal mass than the compact RTSA configurations required for a practical low-grade heat engine.

[0007] Document US 6751958 Bl discloses a method and apparatus for increasing pressure of a feed gas through chemical compression. A feed gas such as natural gas is introduced into a vessel and is absorbed onto material contained therein.

[0008] Document US 9945370 Bl discloses a gas compression system having a compressor, an adsorption device, and a fluid control device. The adsorption device is adapted to output the high-pressure hydrogen gas to the first port and absorb the low- pressure hydrogen gas from the second port. [0009] In view of the foregoing, it would be beneficial to provide a heat engine capable of operating with alternative energy sources, for example with waste heat from various sources, like industrial waste heat.

SUMMARY OF THE INVENTION

[0010] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0011] According to a first aspect of the present invention, there is provided a heat engine comprising a housing comprising a water inlet and a gas inlet in an upper region of the housing, and a water outlet and a gas outlet in a lower region of the housing, a plurality of alternating water channels and adsorbate gas channels within the housing or adsorbate gas channels within a water compartment of the housing, wherein the heat engine comprises nanoporous material as an adsorbent within each of the gas channels.

[0012] Certain embodiments of the first aspect further comprise at least one feature of the following bulleted list:

• the nanoporous material comprises graphene based nanoporous material, activated carbon or zeolite

• the nanoporous material is in the form of pellets or powder

• the housing comprises a first end plate comprising: othe water inlet and the gas inlet in an upper region of the first end plate, and othe water outlet and the gas outlet in a lower region of the first end plate, a second end plate, a plurality of separating plates forming the plurality of alternating water channels and gas channels, wherein the plurality of separating plates is arranged between the first end plate and the second end plate a first resin layer is arranged between the first end plate and the plurality of alternating water channels and gas channels • a second resin layer is arranged between the second end plate and the plurality of alternating water channels and gas channels

• each of the gas channels is filled with CO2

[0013] According to a second aspect of the present invention, there is provided an arrangement comprising a heat engine according to any one of claims 1 - 7, and a system fluidly connected to the gas outlet of the heat engine. According to an embodiment, the system comprises a piston and a cylinder.

[0014] According to a third aspect of the present invention, there is provided a method of manufacturing a heat engine, the method comprising providing a housing comprising a water inlet and a gas inlet in an upper region of the housing, and a water outlet and a gas outlet in a lower region of the housing, providing a plurality of alternating water channels and adsorbate gas channels within the housing or adsorbate gas channels within a water compartment of the housing, and adding nanoporous material as an adsorbent within each of the gas channels.

[0015] Certain embodiments of the third aspect further comprise at least one feature of the following bulleted list:

• the nanoporous material comprises graphene based nanoporous material, activated carbon or zeolite

• the nanoporous material is in the form of pellets or powder

• manufacturing the housing comprises providing a first end plate comprising: othe water inlet and the gas inlet in an upper region of the first end plate, and othe water outlet and the gas outlet in a lower region of the first end plate, providing a second end plate

• the method comprising arranging a first resin layer between the first end plate and the plurality of alternating water channels and gas channels the method comprising arranging a second resin layer between the second end plate and the plurality of alternating water channels and gas channels the method comprising filling each of the gas channels with CO2

[0016] Considerable advantages are obtained by means of the embodiments of the present invention. Embodiments of the invention operate on the principle of thermal swing adsorption (TSA). Adsorption is a process in which a liquid or a gas bonds, either chemically or physically, to the surface of a porous medium. Chemical adsorption, or chemisorption, is linked to the sharing of electrons between the fluid and the porous substrate. It is irreversible and has relatively high enthalpy, resulting in strong interactions. On the other hand, physisorption is related to the weak London and van der Waals forces binding the fluid to the substrate. It is two orders of magnitude weaker than chemisorption bonds; it is also reversible and temperature dependent, occurring only at relatively low temperatures. Most adsorption-based industrial processes involving separation of fluid streams rely on physisorption, and that is the type of adsorption at work in the presently discussed technology.

[0017] The heat engine according to the invention is designed to operate, for example, with CO2 as the adsorbate gas and nanoporous material such as graphene-based substances or solid activated carbon as the adsorbent, and to operate at pressures between 1 and 70 bar, for example between 3 and 15 bar. Activated carbon may be, for example, selected as the adsorbent, because the large total pore volume of activated carbon (AC) enables it to adsorb significant amounts of CO2 in the pressure range.

[0018] Because the equilibrium adsorption of an adsorbate onto an adsorbent depends both on the pressure and temperature of the system, both pressure swing adsorption and temperature swing adsorption processes exist. The invention utilizes low- grade waste heat to drive the process, and therefore temperature swing adsorption is the more suitable process.

[0019] While extensive study has gone into the application of CO2 adsorption for the purpose of gas separation or carbon capture, the application of the thermal swing adsorption process to do work is relatively unexplored. Some applications outside of the gas separation space are adsorption chillers, and heat pumps, both of which essentially replace the compressor component of the thermal cycle with an adsorption bed: the fundamental component is thus the adsorption compressor. [0020] One design parameter to consider when developing technology based on swing adsorption is the cycle time. Technologies that seek to improve the rate of the thermal swing adsorption process fall into the category of rapid thermal swing adsorption (RTSA). RTSA is challenging due to the generally low thermal conductivity of available adsorbents; therefore, creative methods must be applied to reduce the heat transfer resistance to the adsorbent and enable fast adsorption-desorption cycles. A demonstrated RTSA process uses multiple modules consisting of hollow fiber sorbents to separate water from a feed stream. The geometry of the hollow fiber sorbents placed within a reactor resembles the tubes of a shell and tube heat exchanger and enabled rapid heat transfer in the modules; heat regeneration between modules allowed reduced thermal energy consumption. One previous attempt employed similar hollow fiber sorbents and a multibed design with heat transfer between beds for a CO2 capture process. One experiment uses the term adsorbent heat exchanger (adHEX) to describe a heat exchanger (HEX) that has been coated in a thin layer of adsorbent to improve heat and mass transfer to the adsorbent, juxtaposed to a typical “fixed bed” in which adsorbent beads are simply packed into a large container. In this application, the term adHEX refers to any conventional HEX that has been adapted to contain an adsorbent material. A review of adHEXs that use adsorbent coating for adsorption heat pumps and chillers finds that the heat and mass transfer of consolidate beds, binder-based coatings, and in-situ direct synthesis coatings is better than for fixed adsorbent beds, though most of the practical applications of these coatings has been with zeolite-based adsorbents. In this invention nanoporous material such as an AC adsorbent in pelleted form is placed inside an existing heat exchanger without the need for coating technology.

[0021] The novelty of this invention lies both at the system level in the application of rapid thermal swing adsorption to do work in a low-temperature heat engine, as well as at the component level in the mechanical addition of activated carbon pellets to a heat exchanger to enable rapid cycle times.

[0022] The basic physical concept in this invention is the rapid heat transfer to and from a space that is filled with CO2 gas and activated carbon. To achieve this, AC is added to an indirect HEX. Both shell and tube (ST) and plate and frame (PF) type heat exchangers are tested. For each reactor geometry, two forms of AC are compared: pelleted and powdered. CO2 gas is added into the same region as the AC, where it can freely adsorb or desorb onto the AC as the temperature changes. Water flows in the other region of the HEX to indirectly exchange thermal energy with the CO2 space.

[0023] For the case of the ST HEX, water flows through the shell, while the tubes are filled with AC and CO2. In the PF HEX, plates alternate between the water domain and the CO2 space. Both the ST and the PF HEXs are lab scale: the CO2 space is approximately 0.5 liters in both cases and can be entirely filled with just 82 grams of activated carbon material.

[0024] The present work demonstrates a lab-scale heat engine that (i) uses CO2 on activated carbon at ~3 bar start / up to ~12 bar produced by a rapid thermal swing in a 0.5 L adHEX filled with 82 g AC, (ii) integrates the adsorption reactor with a piston/ cylinder to extract mechanical work and reports PV cycles, and (iii) provides experimental energy accounting that identifies parasitic losses and practical mitigation paths (welded plate HEX, insulation, higher operating pressures, inter-reactor heat regeneration). These features distinguish it from both (i) Battelle’s adHEX/separation emphasis and (ii) classical PSA/TSA separation patents focused on gas purification rather than energy conversion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIGURE la illustrates a schematic view of a heat engine in accordance with at least some embodiments of the present invention,

[0026] FIGURE lb illustrates a schematic view of another heat engine in accordance with at least some embodiments of the present invention,

[0027] FIGURES 1c, Id, le and If present lab images of the HEX structure with the adsorbent present,

[0028] FIGURE 2a illustrates a schematic view of an experimental setup and key components,

[0029] FIGURE 2b presents a laboratory image of a heat engine setup using the PF adHEX configuration,

[0030] FIGURE 3. presents the expansion pressure as measured by inlet Pl and cylinder P3 pressure sensors, for pelleted (a) and powdered (b) AC modes of the ST HEX, [0031] FIGURE 4. presents the PV diagrams for selected cycles for each engine configuration: (a) shows an open PV diagram for the ST HEX with pelleted AC; (b) demonstrates a narrower PV diagram for the ST HEX with powdered AC due to flow constrictions during expansion; (c) PF HEX with pelleted AC; (d) the PF HEX with powdered AC resulted in wavy expansion and compression in the PV diagram due to extreme flow constrictions within the reactor,

[0032] FIGURES 5a-c show a comparison of the pressure rise rate in both reactor types during the heating phase, with and without different forms of AC,

[0033] FIGURE 6a compares the rise in pressure rate while having no AC, pellet and powder form of AC in PHEX type of reactor. Figure 6b compares the rise in pressure rate while having no AC, pellet and powder form of AC in STHEX type of reactor.

EMBODIMENTS

[0034] In FIGURE la a schematic view of a heat engine 1 in accordance with at least some embodiments of the present invention is illustrated. The heat engine 1 comprises a housing 2 comprising a water inlet 3 and a gas inlet 4 in an upper region of the housing 2. The housing 2 further comprises a water outlet 5 and a gas outlet 6 in a lower region of the housing 2. Furthermore, the housing 2 comprises a plurality of alternating water channels 7 and adsorbate gas channels 8 within the housing 1. The heat engine 1 comprises nanoporous material 9 as an adsorbent within each of the gas channels 8. For example, the nanoporous material 9 may comprise graphene based nanoporous material, activated carbon or zeolite. The nanoporous material 9 may be in the form of pellets or powder, for instance. Each of the gas channels 8 is typically filled with CO2. Each of the water channels 7 is filled with water. The waste heat is typically provided in the form of hot water. Waste heat may also be provided in gaseous form. The adjacent flows of water through the water channels 7 and gas through the adsorbate gas channels 8 comprising the nanoporous material 9 result in increasing the gas pressure which can be used by an external system arranged downstream of the gas outlet 6.

[0035] According to the embodiment shown in FIGURE la, the housing 2 may comprise a first end plate 10 comprising the water inlet 3 and the gas inlet 4 in an upper region of the first end plate 10. Additionally, the housing 2 may comprise the water outlet 5 and the gas outlet 6 in a lower region of the first end plate 10. Further, the housing 2 may comprise a second end plate 11 opposite to the first end plate 10. Furthermore, the housing 2 may comprise a plurality of separating plates 12 forming the plurality of alternating water channels 7 and gas channels 8. The plurality of separating plates 12 may be arranged between the first end plate 10 and the second end plate 11. A first resin layer 13, for example an epoxy layer, may be arranged between the first end plate 10 and the plurality of alternating water channels 7 and gas channels 8. A second resin layer 14, for example an epoxy layer, may be arranged between the second end plate 10 and the plurality of alternating water channels 7 and gas channels 8.

[0036] FIGURE la outlines how the adsorbing material and heat transfer fluid are arranged in the HEX. FIGURE la shows a representation of the plate and frame adHEX developed for this work. Plate cassettes alternate between water flow channels 7 and adsorbent gas channels 8, which contain CO2 and, for example, activated carbon. Insulating epoxy is used near the end plates 10, 11 to avoid excessive heat transfer to end plates.

[0037] In FIGURE lb a schematic view of another heat engine 1 in accordance with at least some embodiments of the present invention is illustrated. FIGURE lb shows the shell and tube adHEX. AC and CO2 fill the tubes in the HEX, while water flows around the tubes through the shell portion.

[0038] FIGURES 1c, Id, le and If present lab images of the HEX structure with the adsorbent present. FIGURE 1c shows the filling of the PF adHEX with Maxsorb III AC pellets. FIGURE Id shows the internal structure of the ST HEX. FIGURE le shows the assembled PF adHEX, which is approximately 60 cm in length, and FIGURE If shows the assembled ST adHEX, approximately 40 cm in length.

[0039] In FIGURE 2a a schematic view of an experimental setup and key components is illustrated. The Water Pump frequency and Cold Source pressure are set such that the flow rate for hot and cold water is the same, at approximately 0.2 1/s. The experiment is run in six phases: vacuum, precooling and filling, heating, expansion, cooling, and compression.

[0040] Vacuum phase [0041] The purpose of the vacuum phase is to desorb as much gas as possible from the reactor and remove it from the system, as well as remove any moisture that may have developed inside the reactor. During the vacuum phase, the electric heater is turned on and the hot tank is allowed to come up to the set temperature of 75 °C. Valves V2 and V4 are opened, and the Water Pump is turned on, which activates the heating loop of the system. V6 is also opened, and the Vacuum Pump is turned on. The phase lasts for 240 seconds as gas and moisture are pulled out of the system. When the phase is complete, V2, V4 and V6 are closed, and the Water Pump and Vacuum Pump are turned off.

[0042] Precooling and Filling phase

[0043] Next, VI and V3 are opened, and pressure from the cold source drives cold water through the reactor. After precooling for 240 seconds, V5 is opened and the reactor is filled with gas to the specified gauge pressure of 3 bars, as measured by pressure sensor P3. The Hydraulic Pump is turned on and the hydraulic pressure of 9 bars is set using computerized control of the pressure reducing valve (PRV), which remains constant during the experiment. At the end of this phase, the heater is allowed to bring the water in the Hot Tank to its set temperature and is then turned off. The phase is complete when the pressure at P3 stabilizes at the specified pressure; valves VI, V3 and V5 are closed.

[0044] Heating phase

[0045] In the heating phase, V2 and V4 are opened, and the Water Pump is turned on, allowing hot water to flow through the reactor. Heat is transferred to the activated carbon space and CO2 is desorbed, increasing the pressure. The heating phase is complete when the pressure at P3 stabilizes at its maximum.

[0046] Expansion phase

[0047] V7 is opened to allow the high-pressure gas to flow into the Cylinder, driving the piston upward. The gas does work against the hydraulic pressure supplied by the hydraulic pump. The expansion phase is complete when the piston reaches its top position, as measured by the distance sensor DI . When the expansion phase is complete, V2, V4 and V7 are closed.

[0048] Cooling phase [0049] VI and V3 are opened to allow cold water to flow through the reactor, removing heat from the activated carbon space. CO2 adsorbs onto the AC, and pressure drops. Because some portion of the original gas is now trapped as high-pressure gas inside the cylinder, the pressure drops to below its initial value. The cooling phase is complete when the pressure at P3 stabilizes at its minimum.

[0050] Compression phase

[0051] In the compression phase, V7 is opened. There is an initial pressure increase at P3 as the hot gas inside the cylinder mixes with the cold gas in the rest of the reactor. The cold loop is continually running, and as the pressure again approaches its minimum the hydraulic pressure supplied by the hydraulic pump is able to push the piston downward. This phase is complete when the piston reaches its bottom position, as measured by DI.

[0052] The heating - compression phases constitute a single cycle, and the system is allowed to cycle for 10 minutes. After 10 minutes, the system is shut down, and the heater in the Hot Tank is turned back on. The power flowing to the hot water heater is measured using F3, and the energy required to bring the tank back to its original temperature at the start of the experiment is recorded. This represents the thermal energy used by the system during the 10-minute run time.

[0053] Test conditions

[0054] The conditions for each test were the same: Each reactor was filled with approximately 82 g of activated carbon, and the starting gauge pressure of the gas in the reactor was 3 bars. The counterpressure supplied by the hydraulic pump was kept constant throughout the experiment at a gauge pressure of 9 bars. Each test was run such that heat was continuously supplied during the heating and expansion steps, and cooling was continuously supplied during the cooling and compression steps. The maximum pressure reached in the reactor during heating, and the rate of pressure change, are based on the reactor geometry, heat transfer, and resulting adsorption dynamics. The hot water temperature at the start of the experiment is set to be 75 °C, while the cold water varies slightly between experiments as it is sourced from the tap; however, the temperature difference between the hot and cold sources was on average approximately 58 °C. The conditions that were held constant across the experiments are summarized in the following table:

[0055] Table 1. Constant parameters.

[0056] Table 1. Constant parameters.

[0057] The thermal efficiency is higher for the configurations with pelleted AC due to the higher net work done by these configurations; however, in all cases the thermal efficiency is low. This low efficiency is due in large part to the parasitic heating losses. A preliminary energy analysis carried out for one experiment of the ST HEX with pelleted AC helps to understand this loss. The tubestack is the cupronickel set of heat transfer tubes and associated baffles within the ST HEX, shown in Figure 1 (d). The tubestack temperature must change before the CO2 gas temperature can change, as heat is transferred through the tubestack between the water and the gas space. The tubestack temperature is not directly measured; however, the high thermal conductivity of the component means it will closely follow the temperature of the water flowing through the HEX; therefore, the outlet water temperature is used as a proxy for tubestack temperature to determine the energy consumed in heating and cooling the tubestack.

[0058] The calculation reveals that over the course of the 10-minute experiment, heating and cooling the tubestack each consumed approximately 0.11 kWh of thermal energy. This dwarfs the 0.00065 kWh output of the system, determined by summing up the work done by the heat engine over the 10-minute experiment period. The parasitic heat losses within the reactor are therefore significant relative to the output of the system. [0059] Other heat losses include the frictional losses associated with piston movement, as well as energy used to change the temperature of other components of the system such as the shell of the HEX, piping, and the AC. The AC has a mass of 82 g; the piping, valves and couplers have a mass of approximately 1265 g; and the shell a mass of 3129 g. It is therefore likely that significant heat is lost in changing the temperature of the HEX shell during each cycle.

[0060] The desorption reaction also consumes some heat during the heating phase, and the adsorption reaction then releases heat which must be carried away during the cooling phase. These reactions thus add to the other heat losses as well. To improve the thermal efficiency of the engine, the useful work must be increased, and other losses must be decreased. The useful work could be increased by increasing the operating pressure of the engine. Additionally, slowing down the expansion and compression phases may allow a higher overall expansion pressure and a lower overall compression pressure, thus increasing the net work done per cycle. Larger expansion volumes may also be possible, which would further increase the work done each cycle. Finally, adding a thermally insulating layer to the inside of the shell to limit heat transfer to the HEX shell could help reduce losses.

[0061] FIGURE 2b presents a laboratory image of a heat engine setup using the PF adHEX configuration:

[0062] (1) CO2 tank, (2) Gas flow meter, (3) Gas valve V5, (4) Manual valve to vacuum pump V6, (5) Cold water inlet valve VI, (6) Water inlet thermocouple, (7) adHEX Reactor, (8) Water flow meter, (9) Gas outlet pressure sensor P2, (10) Cylinder and piston. The boiler and hot water pump are not pictured.

[0063] FIGURE 3. presents the expansion pressure as measured by inlet Pl and cylinder P3 pressure sensors, for pelleted (a) and powdered (b) AC modes of the ST HEX,

[0064] FIGURE 4. presents the PV diagrams for selected cycles for each engine configuration: (a) shows an open PV diagram for the ST HEX with pelleted AC; (b) demonstrates a narrower PV diagram for the ST HEX with powdered AC due to flow constrictions during expansion; (c) PF HEX with pelleted AC; (d) the PF HEX with powdered AC resulted in wavy expansion and compression in the PV diagram due to extreme flow constrictions within the reactor, [0065] FIGURES 5a-c show a comparison of the pressure rise rate in both reactor types during the heating phase, with and without different forms of AC. For all filling regimes, the pressure increased faster for the PF HEX, supporting the general understanding that the PF type of reactor has a higher heat transfer coefficient than the ST type. The observation that the PF configurations generally seem to stabilize at a higher pressure than the ST configurations may indicate that the gas space volume is slightly less in the PF HEX.

[0066] FIGURE 6a compares the rise in pressure rate while having no AC, pellet and powder form of AC in PHEX type of reactor. Figure 6b compares the rise in pressure rate while having no AC, pellet and powder form of AC in STHEX type of reactor.

[0067] When no AC is present in the reactor, the desorption effect is lost, and the pressure increase is due only to an increase in temperature within a fixed volume. In this case the pressure increase is approximately 25 %, from 4 to 5 bars. With the presence of AC, however, the increase in temperature also causes desorption of CO2 gas, effectively adding gas to the space and increasing pressure significantly more. Configurations with 82 g of AC saw an average increase in pressure of 223 %, from 4 bars to 12.9 bars, with the supplied temperature increase of 58 °C. For the PF HEX, the pelleted AC resulted in a larger pressure increase than the powdered AC — this may be related to gas flow constrictions caused by the powdered AC. Because gas is unable to flow freely through the adsorption bed, there may be localized regions of higher and lower pressure. For the ST HEX, the powdered AC enabled a more rapid pressure increase than the pelleted AC — likely due to the effective thermal conductivity of the pelleted AC: In the ST HEX, AC pellets were added loosely into the tubes of the HEX, which allows void space between pellets. This likely reduces the effective thermal conductivity of the gas space, resulting in longer heating times and thus slower pressure increases. In contrast, pellets are pressed and even crushed tightly together into thin sheets within the PF HEX, likely allowing a higher effective thermal conductivity.

[0068] The design of the ST HEX enabled us to place a thermocouple partially inside the reactor chamber; using this in combination with the pressure sensors, time- stamped pressure and temperature data was acquired during the experiments with the ST HEX + Pelleted AC configuration. [0069] The system studied in this work generally demonstrates a pressure increase from 4 bar to 12 bar absolute when going from approximately 10 °C to 70 °C over a heating period that lasts 20 s to 30 s. This 8-bar pressure increase is related to the net work done by the system, as shown in the PV diagrams of Figure 4. If larger pressure increases were achieved, then it is feasible that more work could be done during each cycle. The model can be used to predict the system pressure increase associated with different initial pressures or heating rates, and therefore can act as a design tool for future versions of the engine.

[0070] This work describes a lab scale heat engine capable of running on low temperature waste heat, based on the principle of thermal swing adsorption. The device considered represents a proof-of-concept for the heat engine, showing that low grade waste heat can be converted to mechanical work through the described process. Two different HEX geometries were considered, as well as two different forms of AC.

[0071] Adding just 82 g of activated carbon material to the 0.5 L gas space of a small heat exchanger enables a pressure increase from 4 bars to over 12 bars as the temperature is increased by 58 °C. In contrast, the same temperature increase caused a pressure increase from 4 bars to only 5 bars when no activated carbon is present. The addition of the activated carbon material thus significantly increases the system’s ability to do work.

[0072] Heating and cooling times are faster for the PF HEX than the ST HEX due to the higher overall heat transfer coefficient of the PF HEX.

[0073] Expansion and compression times are faster for the pelleted AC than the powdered AC due to free gas flow through the pelleted medium.

[0074] Work per cycle is lower when using powdered AC, since the constricted gas flow results in lower average expansion pressure.

[0075] The optimal configuration was a PF HEX with pelleted AC, which benefited from both fast cycle times and relatively high cycle work.

[0076] For all configurations the thermal efficiency was extremely low due to the large proportion of parasitic heat losses due to the indirect heating design. [0077] A 0-dimensional system model based on the D-A equation and the ideal gas law is able to predict the reactor pressure as temperature increases, with reasonable accuracy.

[0078] The system demonstrates a capability to do work and an impressive peak power delivery; however, its weakness lies in low thermal efficiency. Because the system is designed to run on waste heat that would otherwise go unused, its thermal efficiency is less relevant. To improve thermal efficiency to more competitive levels, cycle work needs to be increased lOOx while keeping thermal input relatively constant. To work towards this goal, future versions of this system should use a welded plate heat exchanger with pelleted AC. This would preserve the rapid heat transfer enabled by the PF HEX and the free gas flow allowed by the pelleted AC, while granting significantly higher operating pressures. The gasketed PF HEX used in this work is highly susceptible to leakage at higher pressures due to the large amount of gasketed area, and the ST HEX is limited by lower heat transfer rates. A welded plate HEX may overcome these challenges. Additionally, insulating layers could be used to reduce heat transfer to the shell of the HEX during the cycle. Finally, if future versions include multiple reactors, heat regeneration between components could be implemented to improve efficiency.

[0079] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0080] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0081] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and examples of the present invention may be referred to herein along with alternatives for the various components thereof It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0082] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0083] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0084] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[0085] At least some embodiments of the present invention find industrial application in pressure generation from waste heat. REFERENCE SIGNS LIST heat engine housing water inlet gas inlet water outlet gas outlet water channel adsorbate gas channel nanoporous material first end plate second end plate separating plate first resin layer second resin layer water compartment

Claims

CLAIMS:

1. A heat engine (1) comprising:

- a housing (2) comprising o a water inlet (3) and a gas inlet (4) in an upper region of the housing (2), and o a water outlet (5) and a gas outlet (6) in a lower region of the housing (2),

- a plurality of alternating water channels (7) and adsorbate gas channels (8) within the housing (2) or adsorbate gas channels (8) within a water compartment of the housing (2),

- wherein the heat engine (1) comprises nanoporous material (9) as an adsorbent within each of the gas channels (8).

2. The heat engine according to claim 1, wherein the nanoporous material (9) comprises graphene based nanoporous material, activated carbon or zeolite.

3. The heat engine according to claim 1 or 2, wherein the nanoporous material (9) is in the form of pellets or powder.

4. The heat engine according to any one of claims 1 - 3, wherein the housing (1) comprises

- a first end plate (10) comprising: o the water inlet (3) and the gas inlet (4) in an upper region of the first end plate (10), and o the water outlet (5) and the gas outlet (6) in a lower region of the first end plate (10),

- a second end plate (11),

- a plurality of separating plates (12) forming the plurality of alternating water channels (7) and gas channels (8), wherein the plurality of separating plates (12) is arranged between the first end plate (10) and the second end plate (11).

5. The heat engine according to claim 4, wherein a first resin layer (13) is arranged between the first end plate (10) and the plurality of alternating water channels (7) and gas channels (8).

6. The heat engine according to claim 4 or 5, wherein a second resin layer (14) is arranged between the second end plate (10) and the plurality of alternating water channels (7) and gas channels (8).

7. The heat engine according to any one of claims 1 - 6, wherein each of the gas channels (8) is filled with CO2.

8. An arrangement comprising:

- a heat engine (1) according to any one of claims 1 - 7, and

- a system fluidly connected to the gas outlet (6) of the heat engine (1).

9. The arrangement according to claim 8, wherein the system comprises a piston and a cylinder.

10. A method of manufacturing a heat engine, the method comprising:

- providing a housing (2) comprising o a water inlet (3) and a gas inlet (4) in an upper region of the housing (2), and o a water outlet (5) and a gas outlet (6) in a lower region of the housing (2),

- providing a plurality of alternating water channels (7) and adsorbate gas channels (8) within the housing (2) or adsorbate gas channels (8) within a water compartment of the housing (2),

- adding nanoporous material (9) as an adsorbent within each of the gas channels (8).

11. The method according to claim 10, wherein the nanoporous material (9) comprises graphene based nanoporous material, activated carbon or zeolite.

12. The method according to claim 11, wherein the nanoporous material (9) is in the form of pellets or powder.

13. The method according to any one of claims 10 - 12, wherein manufacturing the housing (1) comprises

- providing a first end plate (10) comprising: o the water inlet (3) and the gas inlet (4) in an upper region of the first end plate (10), and o the water outlet (5) and the gas outlet (6) in a lower region of the first end plate (10),

- providing a second end plate (11),

- providing a plurality of separating plates (12) forming the plurality of alternating water channels (7) and gas channels (8), wherein the plurality of separating plates (12) is arranged between the first end plate (10) and the second end plate (11).

14. The method according to claim 13, the method comprising arranging a first resin layer (13) between the first end plate (10) and the plurality of alternating water channels (7) and gas channels (8).

15. The method according to claim 13 or 14, the method comprising arranging a second resin layer (14) between the second end plate (10) and the plurality of alternating water channels (7) and gas channels (8).

16. The method according to any one of claims 10 - 15, the method comprising filling each of the gas channels (8) with CO2.