Renewable power generation from thermal energy of ambient air

Abstract

Conventional power generation systems and combustion engines are inherently inefficient and as a result release enormous amounts of waste heat into the atmosphere. They also emit large amounts of toxic gases and dangerous pollutants. This invention provides a new method and process for generating power with a considerably enhanced thermal efficiency and from a renewable energy source previously untapped. The invention is a thermodynamic system which converts low-grade heat of ambient air into useful mechanical work. It essentially consists of a novel waste heat recovery (WHR) cycle, an organic rankine cycle (ORC), and a Heat Pump unit. This technology has a broad range of applications in large-scale power generation, seawater desalination, propulsion systems onboard ships, HVAC systems, and in other areas where it could be practically deployed.

Description

Title of invention: Renewable Power Generation from Thermal Energy of Ambient AirTechnical field

[0001] The present invention relates to a thermodynamic system and process for power generation utilizing the renewable thermal energy of ambient air.Background art

[0002] Traditional power plants using fossil and nuclear fuels as well as conventional combustion engines such as gasoline, diesel, jet, and other heat engines convert thermal energy of fuels in the form of heat into useful mechanical energy. A relatively small portion of the initial thermal energy (30-50%) can be converted to useful energy. A big portion (50-70%) has to be dissipated or rejected to the outside. Inevitably they all have this "heat rejection" process in common. For instance, in a steam cycle power plant this is principally the heat of condensation rejected to the atmosphere in order to return low temperature steam back to liquid water. Heat dissipation and rejection is a fundamental and integral part of any thermodynamic power generation cycle, limiting thermal efficiency of the system.

[0003] Considering the tremendous amounts of wasted energy in conventional power generation systems and the adverse effects they have on fuel efficiency and on the environment, the importance and the need for waste heat recovery (WHR) or eliminating altogether by switching to alternative renewable options becomes clearly evident.

[0004] There are also technical challenges with traditional renewable sources of energy. Solar energy is available only during the day when sky is clear, necessitating electrical energy storage for night-time. Converting ocean thermal energy (OTEC) and wave energy to electricity entails installation and maintenance of expensive infrastructure in rough seas with low power outputs. Aside from costly onshore and offshore infrastructure, harnessing energy from intermittent winds is also unreliable as there are times with no winds. Tapping into geothermal reservoirs in remote areas with negligible power outputs proves not economically viable. Energy-intensive and air pollutant biofuels make them the least favorable option among renewables. Raindependent hydropower is also not reliably available in places with droughts and low annual precipitation.

[0005] The transfer of electrical energy produced from almost all these sources to consumers requires long distance transmission lines because of their availability in certain geographical locations resulting in costly infrastructure and energy losses. Whether fossil, nuclear, or renewable, present sources of energy and the power generation methods using these sources come with inherent limitations, energy losses and inefficiencies.Summary of the invention

[0006] The invention disclosed here is a thermodynamic cycle and system for extracting thermal energy from ambient air and converting it into mechanical energy. Unlike other sources of renewable energy which are available in certain areas and during certain times, air is readily available and abundantly present everywhere. This makes it an ideal sustainable and clean energy source, capable of storing and delivering enormous amounts of renewable thermal energy.

[0007] The present invention is a power generation system, essentially consisting of 3 main units: a conventional power generating unit known as Organic Rankine Cycle (ORC), a conventional heat pump unit, and a novel waste heat recovery (WHR) cycle. An ORC unit works similar to a steam cycle widely used in most power plants except for its working fluid which unlike water can evaporate and boil at temperatures under 100C, creating enough pressure to turn a turbine. The WHR cycle captures the rejected heat from the condenser of ORC unit and transfers it to the evaporator / boiler of the same unit to be reused. This significantly increases overall thermal efficiency. The heat pump unit absorbs thermal energy from ambient air and delivers it to the system to be converted into mechanical energy. Figure 1 illustrates the invention.

[0008] The application of this WHR cycle along with the ORC and the heat pump enables us to effectively tap into a source of renewable energy previously considered "low-grade" heat and not practically and efficiently useable with existing technologies. Phasing out and replacing traditional energy-intensive and inefficient combustion engines as well as the nuclear and fossil fuel power plants, which are the major sources of toxic emissions and hazardous pollutants, with this technology are some of the benefits and goals of application of this invention. It could also be used to simultaneously generate renewable power and desalinate seawater and adapted to function as chilled water generator for HVAC systems.Brief Description of Drawings

[0009] Figure 1 illustrates the invention with reference numbers identifying the essential components and elements of a practical thermodynamic system for generating renewable power from thermal energy of ambient air.

[0010] Figure 2 supplements figure 1 by providing an example of the same system with actual conditions and performance data. It helps persons skilled in the art to better understand the invention and accordingly be able to design components for making and using it.

[0011] Figure 3 depicts a theoretical / hypothetical waste heat recovery (WHR) cycle for a typical thermodynamic power generation system.

[0012] Figure 4 illustrates an embodiment of the invention with reference numbers identifying its main components. It helps persons skilled in the art to construct, fabricate, and carry out the best mode of the invention.

[0013] Figure 5 shows an embodiment of the invention similar to figure 4 for combined renewable power generation and seawater desalination. It features a once-through water line instead of a circulating closed loop one.

[0014] Figure 6 supplements figure 5 by providing an example of the same embodiment with actual performance and output data.

[0015] Figure 7 shows an embodiment of the invention modified and adapted for generating chilled water for HVAC systems.

[0016] Figure 8 supplements figure 7 by providing an example of the same embodiment with actual performance and output data.

[0017] Figure 9 and figure 10 further supplement figure 1 by providing more examples of the same system with actual conditions and different performance data. This helps persons skilled in the art to make and use the invention with optimized designs and enhanced performances.Detailed Description of the Invention

[0018] To generate electrical energy at power plants and mechanical power for propulsion in cars, trucks, airplanes, trains, and ships; stored potential energy of fossil, organic, or nuclear fuels has to be converted into mechanical energy in the form of useful work. Accordingly these power generation systems work based on well-known closed or open thermodynamic cycles. Thermal energy of the fuel as heat is added to and rejected from a working fluid (water, air, or similar fluids) respectively in processes defined as heat addition at a hot source / reservoir and heat rejection at a cold sink / reservoir. The goal is to convert a maximum percentage of added heat into useful mechanical work and to minimize waste heat.

[0019] Thermal efficiency, the percentage of useful work or energy able to be extracted from heat addition is inherently a limiting factor in all thermodynamic cycles. A substantial portion of added heat at a higher temperature has to be rejected at a lower temperature in order for the working fluid to return to its initial state to complete the cycle and to continuously repeat the processes. A higher thermal efficiency means more useful work / energy has been extracted from the same input energy and consequently less waste heat / energy has been rejected to the surrounding environment. Heat rejection during power generation and the subsequent loss of valuable energy is a fundamental thermodynamic principle essential for continuous operation of thermal cycles.

[0020] Recovering and reusing waste heat / dissipated energy to generate more useful work is strongly desired. However, from a thermodynamic perspective retrofitting power generation systems with existing waste heat recovery (WHR) technologies such as employing ORC units will not technically yield significant increases in overall efficiency. For example, a combustion engine with 30% efficiency dissipates 70% of thermal energy mainly via engine's cooling system and hot exhaust gases. It can be equipped with a compact auxiliary ORC unit to capture and reuse its waste heat, converting around 7-12% of it to mechanical power. This means almost 90% of that 70% heat still goes to waste, with overall efficiency increasing from 30% to 37%, still 63% of initial energy goes unused. That is why application and utilization of WHR systems will not always make economic and engineering sense considering the new challenges they present and the little value and advantage they bring overall.

[0021] To better explain and understand the core and essence of the invention presented here and the underlying principles of its operation, let's consider and analyze the theoretical performance of a typical ORC power generation system with a hypothetical waste heat recovery (WHR) system as illustrated in Figure 3. As defined in thermodynamics, heat reservoirs and sinks have immense thermal capacities capable of supplying or absorbing large amounts of heat with no noticeable change in their respective temperatures. In thermodynamic cycles, a condenser or boiler / evaporator can act as an idealized heat source or sink by continuously absorbing heat from one working fluid or source and releasing it to another.

[0022] Referring to Figure 3, starting the power generation cycle from point E, initially the low- pressure low-temperature liquid working fluid is pumped to higher pressure from E to F by a pump consuming lkw of energy. Next, lOOkw of heat is added to the working fluid from F to G by the boiler / evaporator, causing the liquid to boil and evaporate into high-pressure gas. From G to H, high-pressure high-temperature gas then goes through expansion via a turbine / expander, generating 12kw of useful work. Finally to return to its initial state, the working fluid loses and dissipates 89kw of heat from H to E in a condenser.

[0023] The ORC works similar to a steam Rankine cycle. Unlike water, its working fluid has a much lower boiling point, able to be boiled and evaporated from a liquid phase to high-pressure vapor with heat sources at temperatures under 100C. The cycle's thermal efficiency is expressed as the ratio of Net Output Work to Input Heat.

[0024] Efficiency = (Net Output Work / lnput Heat) x 100% = (12-1 kw / lOOkw) x 100% = 11%. This means 89% of input energy is being lost / rejected. It would be ideal if this amount of wasted low- grade heat could be reused to produce more power in the same or in another similar cycle.

[0025] Here an ideal waste heat recovery (WHR) cycle would be an energy carrier cycle with its own working fluid or fluids, absorbing 89kw of low-grade heat from A to B from the power generation cycle's condenser. A third cycle, a heat pump via its condenser adds 13kw of heat to the WHR cycle's fluid from B to C bringing total energy carried to 102kw at point C. High- temperature WHR fluid will then enter and exit the boiler / evaporator of the power generation cycle from C to D releasing lOOkw of heat to its working fluid. Finally it will return to its initial state. 2kw of heat from the entire system is assumed to have been lost to the outside.

[0026] The heat pump unit working in reverse requires external work input to extract and transfer heat from a cold to a hot reservoir. By evaporating from low-pressure liquid to low- pressure gas through an evaporator, the working fluid absorbs 9kw of heat from ambient air from I to J. Low-pressure gas will then goes through compression from J to K by a mechanical compressor consuming 4kw of power from the power generation cycle. From K to I, the high- temperature high-pressure gas will release 13kw of heat to the WHR cycle's working fluid, condensing back to high pressure liquid and finally to low-pressure liquid after passing through an expansion valve.

[0027] It is worth noting the difference in the amount of heat entering the system before and after implementing the WHR. Net Input heat from an external source to the system is now 9kw and not lOOkw as was the case with first scenario (no WHR). 89kw of waste heat was captured and reused in the same power generation cycle. With the WHR, the net output work is 12-1-4= 7kw which is lower than llkw.

[0028] The new combined thermal efficiency would be: Net Output Work / lnput Heat x 100%= (12-1-4 kw / 9kw) x 100% = 77%. This means 23% of input energy is now being lost / rejected as opposed to 89% with no WHR. More importantly the input heat was extracted from the surrounding air which is renewable.

[0029] Referring back to Figure 3, for the low-grade waste heat to be carried and transferred from a low to a high temperature point (from B to C), the WHR circulation cycle would not be able to practically achieve that goal using only one working fluid. It may even sound impossible to do so unless it consumes the entire useful work it generated when heat flowed from the hot to the cold source in the power generation cycle, leading to a zero work output. The present invention focuses entirely on solving this difficult problem and providing a feasible solution to realistically overcome this challenge within the established thermodynamic boundaries and principles.

[0030] Referring to Figure 1, the invention which is a system for renewable power generation from thermal energy of ambient air is presented with a practical WHR cycle. Two fluids, air and water working in tandem and flowing in opposite directions (counter-flow) in a closed loop, capture the entire heat from condenser of the ORC unit and transfer it to the evaporator / boilerof the same unit to be reused. It is the practical and functional version of the WHR cycle as illustrated in Figure 3.

[0031] To fully understand and analyze the WHR system illustrated in Figure 1, it's worth noting the importance and functionality of heat exchangers, specifically the counter-flow type. A counter-flow heat exchange process allows optimum heat and energy transfer to happen between two fluids of different temperatures. By creating a consistent and more uniform temperature difference, counter-flow heat exchangers are the most effective design for efficient energy exchange and heat recovery. One fluid could enter hot and exit cold, conversely another fluid could enter cold and exit hot, transferring maximum energy from the hot to the cold fluid.

[0032] In indirect-contact counter-flow heat exchangers, the two fluids are separated by a conductive physical barrier such as tubes. In contrast, direct-contact heat exchangers bring the two fluids into direct physical contact, facilitating the exchange of energy (sensible and latent heat) and mass. Evaporative cooling towers widely used in industrial processes and HVAC systems are a common example of such devices.

[0033] Referring to Figure 1, cold water starts its process by entering the indirect-contact air-to- water counter-flow heat exchanger (5) receiving energy from the incoming warm humid air, increasing in temperature and exiting as cool water. It will then enter heat exchanger (6) which is the condenser unit of the power generating ORC, absorbing the entire waste heat. Having absorbed energy, warm water now enters another indirect-contact air-to-water counter-flow heat exchanger (7) and absorbs more heat from the incoming hot humid air. Hot humid air releases significant amount of latent heat through condensation as well as sensible heat by losing its temperature, causing water to heat up.

[0034] Hot water exits (7) and enters another indirect-contact air-to-water counter-flow heat exchanger (9) to receive additional energy from the incoming hot humid air. With a higher physical temperature, hot water exits (9) and enters heat exchanger (11) which is the condenser unit of an auxiliary heat pump placed between the two streams. Through cooling and condensation, heat and energy transfer occurs naturally from the hot humid air to cold, warm, and hot water in heat exchangers (5)-(7) and (9). As water stream rises in temperature and approaches that of the incoming air, this natural process gradually grows slower and slower. Thehigher the temperature difference, the faster the rate of heat / energy transfer from the hot or warmer fluid to the cold or cooler fluid.

[0035] The auxiliary heat pump unit absorbs latent heat of condensation from the hot humid air through its evaporator unit (10) and pumps it up to the condenser (11) to be released and transferred to the water stream. Hot water exits (11) and then enters heat exchanger (14) which is the condenser unit of the main heat pump cycle, receiving additional energy. The water stream increases in temperature incrementally following each passage through heat exchangers (5)-(6)- (7)-(9)-(ll) and (14).

[0036] Hot water exits (14) and enters the direct-contact air-to-water counter flow heat exchanger (1), losing its entire energy and a portion of its mass to oncoming cold air, causing air to gradually increase in humidity and temperature. Since process in (1) is counter flow the further both fluids move towards the exits, the more their temperatures resemble that of the other. At the exits, there is cold water in one end and hot humid air at the other. Cold water exits (1) and finally arrives back at the same point where it had started to repeat the same process.

[0037] The goal here is preserving the energy potential of the hot water and not diluting it by having air exiting (1) at a temperature much lower than that of the incoming water. It would adversely affect the entire system if that happens. To achieve that goal, there must be proportionality, meaning the flow rate of one fluid must be proportional to that of the other.

[0038] As an example, having 1 m3 / s (=1.22 kg / s) of cold air entering (1) at 15C with relative humidity RH 80% it already contains about 36 kj / kg. For air to exit (1) at 85C with RH 99% it would contain about 2252 kj / kg, an increase in enthalpy of 2216 kj / kg (2252-36= 2216). Total enthalpy change for air is: 2216 kj / kg xl.22 kg / s = 2703 kj / s. Water should enter (1) at a temperature higher than 85C. If it enters (1) at 90C and exits at 15C, it would have a 90-15= 75C temperature drop. To work out its flow rate: Q=m.c. Delta? » m= 2703 / (75x4.18)= 8.62 kg / s. This ensures water flow rate is proportional to air flow rate to obtain the desired humidity and temperature.

[0039] To further explain what processes happen in (1) it is worth noting that as air increases in temperature and humidity it can absorb and store even more energy with little to no change in its physical temperature. The higher its temperature, the bigger its capacity to hold more watervapor and store more energy. Evaporation of water in the presence of air is a complicated and an energy-intensive process, causing both air and water to lose significant sensible heat (drop in physical temperature) and for air to entrain that energy as latent heat (hidden energy) in the form of humidity.

[0040] Referring back to Figure 1, cold humid air begins its process by entering (1), receiving energy from the oncoming hot water, increasing in humidity and temperature, and exiting in a saturated state with a relative humidity RH at or close to 100%. This ensures air is almost at its dew point, the point at which condensation begins to occur. As air exits (1) it approaches a temperature slightly lower than that of the incoming hot water. Hot humid air now contains and entrains almost all the energy from waste heat of ORC which was previously absorbed by the circulating water.

[0041] Hot humid air first enters (10) and releases a small portion of its energy through condensation to the working fluid of the auxiliary heat pump. Exiting (10) it will then enter (9) and undergoes further condensation, releasing more energy while still remaining at a high temperature. By this point it is only a few degrees lower than what it was when it left (1) even though it has already lost significant amounts of energy. Exiting (9) it will next enter heat exchanger (8) which is the evaporator / boiler of the power generating ORC. Here it releases a relatively big portion of its energy through condensation to the working fluid of ORC, causing it to boil and evaporate into hot high-pressure gas. The heat released in (8) is equivalent to the amount QL absorbed in (6) plus the amount of work output Wt from the turbine / expander of ORC plus any heat losses from the ORC unit.

[0042] Still hot and humid, saturated air exits (8) with a lower temperature and enters (7) releasing most of its energy to water through condensation, causing water to heat up. Warm humid air exits (7) and next enters (5) to release the remainder of its energy through further condensation to incoming cold water. Cold humid air exits (5) and finally arrives back at the same point where it had started to repeat the same process.

[0043] To further expand on the key features, processes, and working principles of the present invention as illustrated in Figure 1, the following need particular attention.

[0044] The whole system consists of 3 main units: 1- an ORC power generating unit, 2- a WHR cycle for the ORC, and 3- a heat pump unit for extracting thermal energy from air and supplying it to the system. The ORC operating at a high temperature range TH under 100C for the heat pump to be able to deliver heat and for the WHR to be able to provide hot humid air at that temperature. Water starts to boil at 100C and above, therefore it would not be able to remain in air as vapor anymore. ORC unit also needs heat rejection to occur at a relatively low temperature TL to be able to effectively convert heat to work.

[0045] The ORC is constrained by a low thermal efficiency (7-12%) due to having a low temperature difference between TH and TL compared to other thermodynamic cycles. The purpose and function of WHR cycle is to recover the low temperature low-grade waste heat to be reused in the same ORC unit in order to augment and enhance this low efficiency.

[0046] The WHR cycle as illustrated in Figure 1, comprising two counter flowing streams, air and water, with water initially set to enter (1) at a higher temperature and exit at a lower temperature, likewise air set to enter (1) at a lower temperature and exit at a higher temperature and humidity. It is necessary to create and maintain these initial conditions for the WHR to function. These high and low temperatures of the water and air immediately before and after (1) are different from and independent of the ambient air temperature Tair and its relative humidity. They are also higher than TH in (8) and lower than TLin (6).

[0047] Another important aspect in devising this WHR cycle is the capability of water and air streams to switch their respective energy in a closed loop between two temperature points, high and low. This necessitates a counter-flow arrangement. When one fluid goes from low to high temperature, the other needs to go from high to low and vice versa. Waste heat collection of the ORC is done by warming of one fluid (water) and delivering it by cooling of another fluid (air). While it may appearthat even two water streams in opposing directions would be able to steadily perform that function, the fact is that heat addition or removal would cause a sharp drop or rise in temperature of either fluids, preventing one to reach the low or the high temperature of the other one and vice versa.

[0048] Saturated hot humid air can absorb and release significant amounts of energy and still remain within same high temperature range whereas liquid water would not be as capable.Water, however, works best at low temperature ranges where dry or humid air would not be as capable. The combination of both fluids makes energy excha nge / switchi ng a smooth and efficient process, facilitating the recovery and reuse of ORC's waste heat.

[0049] In the WHR cycle, liquid water absorbs the waste heat of ORC due to its high specific heat Cp of 4.18 kj / kg.K compared to dry air's Ikj / kg.K. If for instance, 42 kj of waste heat from the ORC had to be absorbed, 1 kg of water would rise only about 10C whereas if 1 kg of dry air was used it would rise about 42C. (Q=m.c. Delta? » 42=1x4.18xDeltaT) This makes water an excellent absorber of heat since heat dissipation in the condenser of ORC has to happen in a narrow low range of TL. Air, either dry or humid in low temperatures, would not be suitable for this purpose to stay within a low range of TL as it would rapidly increase in temperature, causing ORC's TLto subsequently rise, leading to lower temperature difference between TH and TL which would result in a much lower thermal efficiency.

[0050] Likewise in the evaporator / boiler of the ORC, there should be a fluid capable of delivering and losing heat while staying within a narrow high range of TH. Here neither liquid water nor dry air would be suitable even though water may sound like a good candidate to do that job as it did in the condenser. If for instance, 46 kj of heat had to be supplied and transferred to the ORC within a narrow range of TH: 80C, 1 kg of water would lose about 11C whereas if 1 kg of dry air was used it would drop about 46C in temperature. However, if 0.44 kg of saturated humid air at 80C with RH 99% were used instead, it would only drop 1C down to 79C and still with RH 99%. This makes humid air an excellent choice to perform that task.

[0051] The work input required for the main heat pump's compressor depends, among other factors, mainly on the temperature difference between the ambient air temperature Tair and the water temperature before entering (1). The greater their difference, the more energy needed to deliver heat to (14) which translates into less output work Wnet from the system. In other words, the system outputs less mechanical work in winter than in summer.

[0052] Important design features need to be taken into considerations in using counter-flow heat exchangers specifically for (5)-(7)-(9) and (l). For an efficient energy exchange and heat transfer, sufficient surface area and contact time and effective thermal insulation is required. To ensure optimum performance and effectiveness, key characteristics such as size, capacity, flow paths,heat loss prevention, and thermal conductivity of materials used in the exchangers are essential.

[0053] The flow rates of both water and air in heat exchanger (1) are of particular importance in determining the capacity for WHR and the work output from the ORC. Water's flow rate is proportional to air's flow rate and vice versa. Calculating, controlling, and adjusting both rates are necessary in designing the system. Increasing or decreasing one causes the other to reflect its effect, impacting their respective exit temperatures. Increasing the flow rate of hot water entering (1) and keeping the flow rate of cold humid air constant will cause water to exit warm and not cold, negatively impacting the entire WHR and rendering it ineffective. Likewise increasing cold humid air flow rate entering (1) and keeping hot water flow rate constant will cause humid air to exit warm and not hot, negatively impacting TH in the ORC and eventually rendering the entire WHR cycle ineffective.

[0054] Within the WHR cycle, it is necessary to use a heat pump unit between the two streams immediately after air leaves (1). As water rises in temperature and reaches close to that of the air, a regular heat exchanger becomes ineffective. The auxiliary heat pump causes the heat transfer to "forcibly" happen by consuming energy which comes from the ORC output work. The amount of heat to be transferred from air to water is correlated with the temperature difference between air exiting (1) and water exiting (9). The lower the better. Having an auxiliary heat pump with properly designed evaporator (10) and condenser (11) is important in reducing the work input to the auxiliary heat pump and increasing the Net output work Wnet leaving the system.

[0055] Having sufficient contact surface area and time in (1) exiting humid air reaches saturation point RH 99-100% at a temperature as closely as it is practically possible to that of the incoming hot water. Failure to do so will cause water exiting (7) and (9) to be in a lower temperature than what it should be which subsequently will cause the auxiliary heat pump to do more work and pump more heat from air stream to water to compensate for that. The more power the auxiliary heat pump unit consumes, the less Net output work leaves the system which is undesirable. This would mean a fairly significant portion of work generated by the ORC is used internally to make up for the inefficiencies in (1) as well as in (7) and (9).

[0056] The main heat pump unit directly extracts heat from the ambient air and indirectly adds that energy to the power generating ORC mainly to replace the heat equivalent to Net outputwork Wnet and the heat losses throughout the entire system, including the WHR. Thermal insulation of the entire system is necessary in order to limit energy losses. Lost or dissipated heat from the system to the outside environment would cause the main heat pump to pump more heat to make up for the energy losses. This means more power is drawn and consumed internally and as a result less Net output work would leave the system. Therefore strong thermal insulation of the entire system is absolutely crucial.

[0057] Figure 2 helps to better understand how this invention works by providing actual data. It illustrates the performance and characteristics of an actual working system. In this example, hot water is set to enter (1) at 90C with a flow rate of 91.94 kg / s and leaves cold at 12C. Cold air is set to enter (1) at 12C with a flow rate of 10 m3 / s (=12.33 kg / s) and leaves hot at 86C with relative humidity RH 99%. As indicated on the drawing, this system would produce a net output power of about Wnet: 332 kw or 33.2 kw per m3of cold air.

[0058] Figure 9 illustrates the performance and characteristics of another system. In this example, hot water is set to enter (1) at 94C with a flow rate of 133.5 kg / s and leaves cold at 12C. Cold air is set to enter (1) at 12C with a flow rate of 10 m3 / s (=12.33 kg / s) and leaves hot at 90C with relative humidity RH 99%. As indicated on the drawing, this system would produce a net output power of about Wnet: 584 kw or 58.4 kw per m3of cold air. A 76% increase in Wnet compared to the system of figure 2.

[0059] Figure 10 illustrates the performance and characteristics of another system. In this example, hot water is set to enter (1) at 97C with a flow rate of 195.25 kg / s and leaves cold at 12C. Cold air is set to enter (1) at 12C with a flow rate of 10 m3 / s (=12.33 kg / s) and leaves hot at 93C with relative humidity RH 99%. As indicated on the drawing, this system would produce a net output power of about Wnet: 987 kw or 98.7 kw per m3of cold air. A 197% increase in Wnet, nearly triple that of the system of figure 2.

[0060] As can be seen from aforementioned examples, Net output work significantly increases as saturated air leaving (1) increases from 86C to 90C and up to 93C. Hotter air contains even more water vapour and therefore absorbs more energy from hot water to reach saturation (RH 100%). This would require much higher water flow rates for higher air temperatures. Despite the fact that air leaving (1) at a higher temperature leads to a higher TH in (8) for the ORC unit whichtechnically would increase its thermal efficiency and subsequently lead to a higher Net output work Wnet, it is actually not the primary goal here.

[0061] Increasing thermal efficiency of the ORC unit alone from 8% to 8.5% and to 10% would not have a significant effect on the overall power output from the system. What is actually happening is that hotter air needs more hot water, this means more cold water leaving (1) would be available for the condenser (6) of ORC. A higher water flow rate m absorbs more heat within a specified temperature range Delta according to formula QL=m.c.Delta?. This directly and significantly increases the capacity of ORC which leads to an overall higher power output regardless of its thermal efficiency. Similarly lowering the temperature of cold water leaving (1) would extend the temperature range Delta? over which water absorbs heat from condenser (6). This would increase the amount of heat absorbed QL in condenser (6) further contributing to a bigger capacity for ORC and as a result greater power output from the system. For instance, a Delta?: 25C means water warming from 12-37C resulting in a QL greater than that of a Delta?: 22C warming from 15-37C.

[0062] Raising humid air temperature and the subsequent rise in hot water flow rate as well as lowering cold water temperature to extend Delta? would require larger surface areas and longer contact times in almost all heat exchangers used in this system, specifically in (1). This entails bigger equipment. There is a tradeoff between higher power output with bigger and more costly equipment and lower power output with smaller and less costly equipment.

[0063] In aforementioned examples, heat losses from the entire system have been approximated to be in the range of 0.2C / s drop in water temperature. Strong and effective thermal insulation is necessary to keep these losses in check.

[0064] The novel WHR cycle as described here plays a pivotal role in this invention by providing a high and a low temperature steady source / reservoir for a power generating cycle such as an ORC to work and operate and for a system to have an overall thermal efficiency comparatively much higher than those of the conventional methods. More importantly, it makes possible the use of low-grade heat mainly from ambient air or alternatively in cold weather and climates from sources such as rivers and seawater, waste heat of industrial processes, and even fossil fuels.Preferred embodiments of the invention

[0065] The present invention, renewable power generation from ambient air's thermal energy as described and presented in Figure 1, can practically be constructed and implemented as the embodiment illustrated in Figure 4.

[0066] Referring to figure 4, the WHR cycle with heat exchanger (1) is best represented by an evaporative cooling / humidification unit (1). Hot water enters a set of sprinklers and is sprayed over a fill media (22) with large surface area which could be made with thin copper or aluminum plates or any other suitable conductive materials. The thin sheets help divide and scatter the falling water into micro streams and droplets as well as help create narrow vertical parallel channels for air stream to pass through, facilitating efficient heat and energy transfer. Cold water collects in tank (3) and is pumped by a water pump (4) to (5).

[0067] The heat exchangers (5), (7), (8), (9) and (10) are best represented by incorporating into a dehumidification unit (2). Intense condensation occurs in unit (2) all the way from top to bottom. Cool water exits (5) leaving unit (2) to enter (6) to absorb waste heat of the ORC. Returning to unit (2) and continuing its path, warm water enters (7) and progressively heats up. Hot water passes by (8) continues up and enters (9) to absorb additional energy, further increasing in temperature. Hot water exits (9) at a temperature only a few degrees lower than that of the oncoming air. Leaving the dehumidification unit (2) hot water next enters (11) to indirectly absorb additional energy from the air stream with the help of an auxiliary heat pump unit.

[0068] The evaporator unit (10) of the auxiliary heat pump located at the inlet and top of unit (2) absorbs energy from the hot humid air which is coming directly from the humidification unit (1). This energy is "forcibly" transferred via compressor (25) to water stream in (11) which is the condenser unit of the auxiliary heat pump. Hot water exits (11) and enters (14) which is the condenser unit of the main heat pump. Here it absorbs the thermal energy which has been extracted from the ambient air in (12). Hot water which has successively and gradually heated up finally enters humidification unit (1) to repeat its process.

[0069] Heat exchangers (5), (7), and (9) preferably could be of finned coil / tube type made withcoppertubes and thin aluminum plates. Likewise evaporators (8) and (10) could also be of finned coil / tube type made with copper tubes and thin aluminum plates.

[0070] Referring back to Figure 4, initially provided cold humid air enters humidification unit (1) and starts ascending through (22) interacting with falling hot water, gradually increasing in temperature and humidity. It exits (1) as hot saturated humid air. Thermally insulated duct (26) conveys it to unit (2) where it initially releases heat to (10) which is the evaporator unit of the auxiliary heat pump. It then continues flowing downward through (9), (8), (7) and (5) releasing more energy through further condensation. The cold condensate collects in tank (23) and is pumped to tank (3) via water pump (19). Cold air duct (27) conveys cold humid air to (1) to repeat its process. Fan (20) moves air throughout the WHR cycle.

[0071] The cold water in tank (3) needs to be initially provided and subsequently maintained cold during the entire operation. Cold water causes cold humid air to exit (5) and subsequently this cold air causes cold water to exit (1). In essence it is a reciprocal and feedback effect where one directly impacts the other and vice versa.

[0072] The ORC unit, similar to the widely used ones, utilizes common HFC refrigerants such as R-134a or R-245fa or any other suitable working fluid. They all boil and evaporate in temperature ranges under 100C creating sufficient pressure to expand in a turbine or expander. A liquid refrigerant pump (17) pumps and pressurizes the working fluid and sends it to the boiler / evaporator (8). High-pressure gas exits (8) and enters and expands in a turbine or expander (16) generating useful work in the form of rotational mechanical energy which can be converted into electricity by spinning a generator (18). Lower pressure gas exits (16) and enters (6) which is the condenser, cooling and changing phase from gas to liquid and releasing all its heat to water stream of the WHR cycle.

[0073] The main heat pump unit comprising an evaporator (12) a compressor (13) a condenser (14) and an expansion valve (15) and a suitable working fluid, provides the input heat to the system. To minimize heat losses and maximize work output, all components including hot and cold air ducts, cold water and condensate tanks, hot and cold water lines, humidification and dehumidification units, turbines and compressors need to be well insulated and, to the extent possible, thermally isolated from each other as well as the outside environment.

[0074] The auxiliary heat pump unit comprising an evaporator (10) a compressor (25) a condenser (11) and an expansion valve (24) and a suitable working fluid facilitates the heat transfer from the hot and humid air to hot water where temperature of water leaving (9) is within close range of the air leaving (1) hence a heat exchanger would not be able to do the job.

[0075] An insulation layer (21) where practicable, encapsulating the entire system would slow and prevent heat losses to the outside, especially in cold environments. The only component to be exposed to the outside environment is (12) and it is best to be located in direct sunlight in stationary applications. That would help reduce the temperature difference between (12) and (14) which, among other factors such as heat loss prevention, would lead to less power needed internally for the heat pump and more power output.

[0076] Another embodiment and application of this invention is illustrated in Figure 5. It is a combined seawater desalination and renewable power generation system. It is the exact embodiment illustrated in Figure 4 only that the circulating process water of the WHR cycle has been replaced by seawater with a once-through configuration. Warm seawater, after passing through a counter-flow heat exchanger (28) and becoming cold, is fed into the system and follows the same path as previously described. It eventually reaches tank (3) as cold brine and leaves the system through (28). Cold condensate collecting in tank (23) leaves the system as freshwater.

[0077] This configuration is able to simultaneously generate renewable power and freshwater. It can be used in coastal areas close to sea or onboard ships. For marine applications the power generated could directly be used through a drive mechanism for the ship's propulsion system, and the freshwater for domestic use by the crew and for other applications onboard the ship. Figure 6 presents an example of this embodiment with actual output data. Input heat to the system can also be extracted directly from warm seawater when air is colder than seawater.

[0078] Another embodiment and application of this invention is illustrated in Figure 7. It can function as a chilled water generator for HVAC systems. It is a simpler version of the embodiment described and illustrated in Figure 4. Only heat exchanger (5) is used in (2). Other components are eliminated.

[0079] Hot ambient air enters the system via an air-to-air heat exchanger (29) commonly knownin HVAC industry as an ERV (energy recovery ventilator) or HRV (heat recovery ventilator) unit. It loses part of its energy to the outgoing cool humid air, dropping in temperature and becoming cool. It will then enter (2) and passes through (5) further cooling and losing its energy to incoming cold water. Cold humid air exits (5) and enters (1) which here functions as an evaporative cooling unit. Cold air comes into direct contact with the falling warm water causing it to evaporate and to chill. Cool humid air exits (1) and finally enters (29) absorbing energy from the incoming hot ambient air and leaving the system warm and humid.

[0080] The initial cold water in tank (3) is pumped to heat exchanger (5) where it absorbs energy from air, causing air to become cold. Cool water which is now slightly warmer than before exits (5) and is supplied either directly or indirectly to HVAC systems. Warm water returns from HVAC systems and enters (1) to be sprayed over the fill media. Cold water finally collects in (3) to repeat the process. Since a portion of water evaporates into air and leaves the system, makeup water is added to the return line. Cold condensate collects in tank (23) and is pumped to (3). To enhance efficiency it is necessary that all cold water tanks and lines, ERV, the evaporative cooling unit, the air cooling unit and ducts as well as chilled water supply lines be thermally insulated. Figure 8 shows an example of this embodiment with actual performance data. End of description.To come up with this invention, the inventor, a curious and visionary mechanical engineer with limited financial resources, has spent years working solo in a basement lab, exploring and experimenting with various methods and processes, often with disappointing results and failed experiments, forced to stop and go back to the drawing board countless times to devise and refine and to start all over again even in the darkest moments, all along determined to bring to fruition a seemingly impossible concept and idea, and to eventually turn a vision into reality, a long and arduous journey indeed!

Claims

ClaimsClaim 1: A thermodynamic system for renewable power generation utilizing thermal energy of ambient air comprising three main units:- an Organic Rankine Cycle (ORC) unit for mechanical power generation;- a Waste Heat Recovery (WHR) cycle configured to capture waste heat from condenser of the ORC unit and transfer and deliver to the evaporator of same ORC; and- a Heat Pump unit configured to extract thermal energy from ambient air and deliver to WHR cycle.Claim 2: The system of claim 1, wherein the WHR cycle consisting of two working fluids, air and water, flowing in opposite directions (counter-flow) and circulating in a closed loop, with water capturing the entire waste heat from the condenser of the ORC (6) and transferring it to the air in (1) to be subsequently delivered to the boiler / evaporator of the ORC (8).Claim 3: The system of claim 2, wherein hot water transfers its entire thermal energy to air through an evaporative cooling and humidification process in a direct-contact counter-flow heat exchanger (1) causing air to become hot and humid and water to become cold.Claim 4: The system of claim 3, wherein hot humid air subsequently transfers its energy back to water through a dehumidification process, causing air to become cold and water to become hot.Claim 5: The system of claim 4, wherein an auxiliary heat pump extracts a portion of thermal energy from hot humid air in (10) and delivers it to process water in (11).Claim 6: The system of claim 1, wherein the Heat Pump configured to optionally capture and extract thermal energy directly or indirectly from sources other than ambient air.Claim 7: The system of claim 2, wherein the WHR cycle configured to optionally replace its circulating process water with a once-through arrangement for simultaneous seawater desalination and power generation.Claim 8: The system of claim 1, wherein the Heat Pump and the ORC units are eliminated and WHR cycle configured and adapted to optionally generate chilled water for HVAC applications.

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