GB2494888A

GB2494888A - Turbine based heat engine

Info

Publication number: GB2494888A
Application number: GB1116309.4A
Authority: GB
Inventors: William Alexander Courtney
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-09-21
Filing date: 2011-09-21
Publication date: 2013-03-27
Also published as: GB201116309D0

Abstract

A turbine based heat engine that transfers energy from a moving fluid to a set of turbine 3 blades, allowing a turbine shaft 4 to do external work. The engine is characterised by the engine operating at a higher efficiency than the maximum theoretical efficiency predicted by the Carrot equation by virtue of the fact that it extracts both sensible heat and bulk kinetic energy from the fluid. The heat engine may comprise a metal walled conduit 1. The heat engine may comprise a circulation pump 2 for driving the working fluid around the system against the resistive force of viscous drag. The working fluid may be a liquid, vapour or a gas. The turbine may be coupled by the shaft to an electricity generator 5. A constricting nose 6 may be added to the front of the turbine blades so that fluid passes through the turbine blades at a higher mean speed than the mean speed when passing through wider parts of the conduit.

Description

Hybrid heat engine

Technical Field

According to the invention, there is provided a turbine based heat engine that transfers energy from a moving fluid to a set of turbine blades, allowing the turbine shaft to do external work, characterised by the engine operating at a higher efficiency than the maximum theoretical efficiency predicted by the Carnot equation by virtue of the fact that the engine extracts both sensible heat and bulk kinetic energy from the fluid.

Brief description of the drawings

Figure 1 gives examples of the basic features of the invention.

Figure 2 is a sketch graph of net power output against time after the circulation pump has been switched on.

Figure 3 illustrates the apparatus used to verify the basic properties of the invention.

Figure 4 is a composite diagram showing some of the possible turbine and circulation pump variations according to the invention.

FigureS shows ajet pump system serving a plurality of turbines.

Figure 6 is a sketch graph showing the power output per unit volume of the turbine enclosing conduit plotted against turbine size.

Figure 7 depicts a closed loop of devices according to the invention.

Figure 8 depicts the first type of heat pump.

Figure 9 depicts a type 2 heat pump.

Figure 10 depicts a type 3 heat pump.

Figure 11 is a flow chart explaining how the invention can be combined with heat pumps to improve the energy efficiency of carbon capture from power station flue gases.

Figure 12 is a flow chart explaining a second method for improving the energy efficiency of carbon capture from power station flue gases.

The prior art

The present inventor, Courtney, has revealed a novel form of closed loop turbine in patent application PCT/08201 1000936. An essential feature of this invention is that a substance phase change occurs inside the body of the invention, releasing latent heat to power the turbine. During the course of experimental work on this prior turbine Courtney discovered the basic principles of a superficially similar turbine, but which has a crucial difference; no substance phase change needs to take place inside the body, shell or conduit that houses the turbine.

Disclosure of the invention

Figure 1 gives examples of the basic features of the invention. It is not intended in any way to limit the shape or size of the invention. Item I is a thermally conducting metal walled conduit, which for prototype research has a diameter of approximately 1 metre. It may be painted man black and have a roughened external surface to assist in heat transfer. Item 2 is a circulation pump used for driving the working fluid round the system against the resistive force of viscous drag. The working fluid may be a liquid, vapour or a gas. For illustrative purposes, the fluid will be assumed to be thy air. Item 3 is a turbine coupled by a shaft 4 to an electricity generator 5. In order to ensure that the turbine shaft does work at a higher rate than the shaft attached to the circulation pump, the air impacting on the turbine blades travels at a significantly higher velocity than it exits the circulation pump blades. This increase in velocity is achieved by adding a constricting nose 6. This preferably, but not essentially takes the geometrical shape of a shell formed by a rotating parabola. A similar shaped tail 7 allows the air to slow down gradually alter transiting the turbine blades. Skilled engineers will be aware that the constriction has similar physical properties to a Venturi constriction such that the fluid cools as it accelerates on traversing as the converging section of the constriction, and then warms as it traverses the diverging section. In this example the circulation pump is coupled to a motor 8. For the device as a whole to produce a net output of power in the form of electricity, the output from the generator 5 must exceed the input to the motor 8. In this example, in the steady state, conservation of energy is achieved by the flow of thermal energy into the device, through the walls of the conduit. The external medium that acts as the heat source or warm reservoir can be solid, liquid, vapour or gas. It could even be a vacuum if heat rays fall on to the conduit and warm it. Fluid media have the advantage that fluid can he pumped around the device or circulation currents exploited to present fresh warm material to the conduit walls at a steady rate, Steam, moist air or any other fluid that can suffer a phase change with the release of latent heat on contact with the walls are particularly effective for maximising the rate of heat flow for a given rate of fluid flow.

Figure 2 is a sketch graph of net power output against time after the circulation pump has been switched on, assuming that the device is initially at the same temperature as its environment and that it absorbs replacement heat through the conduit walls. In the first few moments after the circulation pump has been switched on (1) the temperature gradient across the conduit wails is too low to draw in sufficient heat to make up the difference between the power input to the motor and the power output from the generator. Consequently the air progressively cools. Its density correspondingly increases and its velocity on transiting the turbine blades progressively falls. The kinetic energy of the air impacting on the turbine blades per unit time is a function of air density multiplied by air velocity squared. So the drop in velocity caused by cooling is more effective in reducing power output than the increase in density is in increasing power output. The power output and temperature of the conduit walls both fall until an equilibrium plateau 2 is reached.

On this plateau: Power output from turbine Power input to circulation pump motor + Power loss from system ÷ Net rate of heat flow through conduit walls This equation in collaboration with the above analysis reveals that a power generating device according to the invention acts as a hybrid heat engine that extracts both sensible heat and bulk kinetic energy from the air as it passes through the turbine. Traditionally engineers have used the Carnot equation to calculate the maximum possible efficiency of a heat engine. The thermodynamics text books teach that a heat engine cannot have a higher efficiency than predicted by the Carnot equation.

This equation states that the Maximum possible efficiency of a heat engine = I -(Exhaust temperature T2/Inlet temperature T1) But, the Carnot efficiency equation only takes into account the loss of thermal energy, so a hybrid engine that also reduces bulk kinetic energy can be more efficient than a Carnot engine without violating the laws of thermodynamics.

Figure 3 illustrates the apparatus used to veHf' this discovery, To stabilise the temperature readings an open looped system was used so that the air only made a single transit of the turbine. A 550 watt blower, I was used to draw dry air 2 through a turbine 3 connected to a generator 4. Thermometers S and 6 were used to measure the temperature drop across the turbine. The proof of concept apparatus was so small that the nose and tail 7 and S could be removed without affecting turbine performance. To simpii1' the analysis, the apparatus walls 9 were well lagged to prevent the inflow of heat.

The following table shows a typical set of results.

Power output Temperature drop Predicted Measured Measured (W) across turbine (K) maximum efficiency efficiency efficiency using Theoretical the Carnot maximum ________________ _________________ equation _________________ efficiency 6.7 1.46 0.45% 1,22% x2.7 These results verifS' that the invention isa hybrid heat engine that offers a higher efficiency than the maximum efficiency predicted by the Carnot heat engine equation. The experiments were repeated using moist air with a fbrther improvement in performance noted. In part, this improvement over the Carnot equation is due to the release of latent heat inside the conduit as revealed in the present inventor's earlier application PCT/GB2OI 1000936. But the moist air still cools slightly as it loses moisture and its dew point falls. This has taught us that a latent heat releasing heat engine also suffers a reduction in bulk kinetic energy. The present invention is extended to include the improvement in efficiency when the bulk kinetic energy of a dew point fluid is reduced as it transits a set of rotating turbine blades and its dew point falls.

The following table compares typical results for a dry air and a moist air turbine experiment.

Power output Temperature drop Predicted Measured Measured (W) across turbine (K) maximum efficiency efficiency efficiency using Theoretical the Camot maximum ________________ ________________ _______________ equation _________________ efficiency Dry air turbine 6.7 1.46 0.45% 1.22% x2.7 Moist air turbine 1.25 0.29 0.12 1.33 x 11.1 Figure 4 is a composite diagram showing some of the possible turbine and circulation pump variations according to the invention. The air Will possess angular momentum after passing though the turbine 1. hf a second turbine 2, rotating in the opposite sense is added, the air emerging from the second turbine Will possess far less angular momentum. Likewise by adding two impellor circulation pumps 3 and 4 rotating in opposite senses, the angular momentum of the air emerging from the second pump can be minimised. Items 5 and 6 are two concentric impellor circulation pumps. Pump 5, which motivates the air close to the central axis, rotates at a different frequency to pump 6, which motivates the air close to the conduit walls.

An alternative type of circulation pump could be based on the jet pump principle. A compression pump 7 extracts a fraction of the circulating air at 8, compresses it and re-injects it at 9. Buffer reservoirs 10 and 11 smooth out the rate of extraction and injection.

S

The nose 12 and tail 13 can be made from thermally conducting materials and include hollow cavies. The external fluid, for example steam, which acts as the heat source can enter the cavities via pipes 14 and 15, with cooler fluid and any condensation exiting via pipes 16 and 17.

Figure 5 shows a pair of buffer reservoirs 1 and 2 connected to a pair of compression pumps 3 and 4 operating in anti-phase. The pumps extract air from a plurality of devices or sections of devices according to the invention and then re-inject the air via a plurality ofjet pumps. The inclusion of a plurality of compression pumps further reduces the variations in jet pump air flow and allows a simplification of overall circulation pump design.

Figure 6 is a sketch graph showing the power output per unit volume of the turbine enclosing conduit plotted against turbine size, The curve has a flat peaked maximum which is explained as follows. For small turbines viscous drag is very high so the power output per unit volume is low. For very large turbines the ratio of total conduit surface area to conduit volume is low so the rate at which heat flows in through the conduit wails is insufficient to maintain a large power output. The curve has a flat peak because the reduction in the conduit surface area to volume ratio also forces the engine to run cooler, so the mean temperature gradient across the conduit walls increases, increasing the rate of heat flow into the interior of the conduit.

There are two other ways of shifting the peak to the right: (I) Increase the stagnation pressure of the air inside the conduit, so that its density increases, thereby increasing the kinetic energy of the air on impact with the turbine blades for a given impact velocity, (ii) replace the air with a gas having a higher molecular weight such as carbon dioxide or HFO-1234yf(an air conditioning unit refrigerant developed to help automakers meet 2011 European regulations).

Increasing the molecular weight increases the stagnation density for a fixed gas pressure and temperature.

Molecular weight Relative density at same temperature and pressure.

Air 28.84 1.0 Carbon dioxide 44 1.5 HFO-1234yf 114 4.0 Man illustrative example of a practical application of the invention, a plurality of such devices can be linked in series sharing a common conduit and used for converting the low grade heat stored in steam turbine exhausts into electricity.

Figure 7 depicts a closed loop of devices according to the invention 1 inside a steam condensing chamber 2. The exhaust steam 3 is drawn into the chamber as preceding steam condenses on heat exchange fins such as 4. The latent heat released by condensation acts as the heat source for the turbines. As with other versions of the invention, there are two air cooling mechanisms involved inside the conduit. (i) The air cools when it does work driving the turbines.

(ii) it also cools when its speed increases as it enters the constriction presented by the nose. (Venturi cooling) Consequently the air is at its coolest directly after emerging from a turbine. The tails, for example 5 can beneficially be extended to increase the region where Venturi cooling is most significant.

This condensation chamber version of the invention could be used to improve the safety of nuclear power stations.

Nuclear reactors could run cool for the limited purpose of producing low pressure steam. Compared with conventional reactors, cool running nuclear reactors would be very safe and produce less nuclear waste per unit of electricity. It will be possible to operate the reactors commercially at temperatures where residual nuclear activity after an emergency plant shutdown is insufficient to produce reactor core meltdown.

This condensatioE chamber version of the invention would also be useflul in environments where there is a demand for moist air cooling or air conditioning.

Combined micro-power and solar desalination plants are another option. Solar radiation would be used to partially evaporate brine. A heat engine according to the invention would act as the heat sink, absorbing the latent heat released when the water vapour condensed.

The core invention is extended to include a new class of heat pumps. These would be used to manufacture a phase change fluid such as steam, to power a condensation chamber version of the similar to that depicted in Figure 7.

Three types of heat pump will be described as extensions of the core invention. For the purposes of illustration, the phase change fluid is assumed to be steam, with the term "steam" being used to represent saturated water vapour at any temperature it currently exists at. Two operating temperatures will be referenced for these illustrations: (i) below about 20°C the saturated vapour pressure of steam is negligible for steam manufacturing purposes; (ii) saturated steam exerts a vapour pressure of one atmosphere at 100°C. This is a convenient pressure for the external fluid that supplies heat to the interior of the conduit because it minimise pressure stresses on the condensation chamber walls.

These reference temperatures will be assumed in describing the heat pumps.

FigureS depicts the first type of heat pump, conveniently described as a "type I heat pump". This type captures the heat produced when an elastic fluid is compressed and uses it to generate steam. This steam is then for used as fuel inside the condensation chamber. Item 1 is a compression pump immersed inside a water bath 2, inside a well lagged chamber 3. Gas or vapour at a comparatively low pressure is drawn into the pump at 4 and exits at a higher pressure via pipeS. The heat of compression is used to boil the water to produce steam at the core invention condensation chamber pressure. The steam exits to the condensation chamber at 6. For illustrative purposes, the water boils at 100°C and the compressed fluid exits at a temperature very slightly above 100°C.

Type 2 heat pumps are used to convert heat from donor fluids warmer than about 20°C into saturated steam at the condensation chamber pressure.

Figure 9 depicts a type 2 heat pump. Warm liquid, gas or vapour 1 passes through a chain of lagged water filled evaporating chambers where the donor fluid progressively cools as heat is extracted to boil the water inside the chambers. If the donor fluid is sufficiently warm, the water in the first chamber 2 boils at 100°C and the steam is drawn directly into the condensation chamber via pipe 3. If the water boils at a lower temperature it has to be compressed up to condensation chamber pressure using a type 2 heat pump. The cooled fluid4 exits the final evaporating chamber at about 20°C. In principle, a single evaporating chamber could be used to produce steam at 20°C, but this would be inefficient because the type 2 heat pump would need to compress very large volumes of steam from very low pressures. It is preferable to employ a chain of evaporating chambers, with two chambers (2 and 5) being shown in this illustration. Steam produced in the second and any successive evaporation chambers must be elevated to condensation chamber pressure using a type 2 heat pump.

Type 3 heat pumps are used to convert heat extracted during refrigeration process into steam at the required condensation chamber pressure.

Figure 10 depicts a type 3 heat pump. The illustration shows a warm fluid 1 being refrigerated. The fluid passes through the cold reservoir of the refrigerator 2 and exits as a chilled fluid 3. The refrigeration pump 4 shifts the extracted heat to the warm reservoir 5. An evaporation chamber 6 inside the warm reservoir absorbs heat to produce steam. This is extracted via pipe 7 to a type I heat pump.

The core invention in cooperation with the thee types of beat pump has many industrial applications. Flow charts will be used to illustrate how two different methods of carbon capture from fossil fuel power station flue gases can be converted into net power generation processes.

First method In the amine carbon capture process the CO2 leaves the top of the stripper at about 80°C. It is mixed with saturated water vapour.

Figure 11 is a flow chart explaining how the present invention can be combined with heat pumps to convert the bulk of the heat released by condensing CO2 and water vapour into electricity. Item I is water vapour plus CO2 entering a type 2 heat pump at about 80°C. Water 2 is drained off and steam 3 is drawn into a condensation chamber according to the invention. The residual water vapour and all of the CO2 4, which has now cooled to about 20°C enters a type I heat pump. Here the CO2 is (preferably but not essentially) compressed to its critical pressure. The heat of compression is used to generate a second batch of steam 5 for the condensation chamber. A second type 2 heat pump is used to cool the compressed CO2 and residual water vapour to about 20°C. The first fraction of liquefied CO2 and the residual water 6 is drained off and a third batch of steam 7 is drawn into the condensation chamber. Finally, the compressed CO2 is passed through a type 3 heat pump where it is cooled to well below 0°C so that the bulk of the CO2 8 is liquefied and a fourth batch of steam 9 sent to the condensation chamber.

Second method The cryogenic carbon capture process can be used to capture C02, SO2, and NO2 plus any Hg vapour present. This process requires very higher compression ratios because (for high extraction efficiency) the partial pressure of the CO2 should preferably reach its critical pressure.

Figure 12 is a flow chart explaining the ciyogenic carbon capture process benefits according to the invention.

Item 1 is hot flue gases entering a type 2 heat pump. Water, any Hg present in the flue gases plus dust particles which act as condensation nuclei are drained off(2) and steam 3 is drawn into a condensation chamber according to the invention. The residual flue gases, now cooled to about 20°C. enter a type 1 heat pump. Here the CO2 is (preferably but not essentially) compressed so that its partial pressure is raised to its critical pressure. The heat of compression is used to generate a second batch of steam 4 for the condensation chamber. A second type 2 heat pump is used to cool the compressed flue gases to about 20°C. The first fraction of liquefied CO2, SO2, and NO2 and the residual water 5 is drained off and a third batch of steam 6 is drawn into the condensation chamber. Finally, the compressed flue gases are passed through a type 3 heat pump where they are cooled to well below 0°C so that the bulk of the CO2. SO2, and NO2 7 is liquefied and a fourth batch of steam 8 sent to the condensation chamber. The highly pressurised gas 9 that emerges from this process is mainly nitrogen.

Optionally, the compressed nitrogen can be liquefied by passing it through a further Type 3 heat pump and then stored. During periods of peak power demand unwanted heat can be added to convert the nitrogen back into a highly pressurised gas for driving a secondary conventional turbine. The required heat could come from a wide range of industrial processes including computer server centre cooling, food chilling, freeze desalination of sea water and the production of synthetic snow and ice for year round winter sports centres.

One option wouid be to use the liquefied nitrogen to cool the power transmission cables and then use the nitrogen to drive conventional turbines at remote sub stations.

The present invention is extended to include the following: * Versions of the invention that that draw in heat from a wanner external environment and also benefit from the internal release of latent heat as revealed in the present inventor's prior patent application * Versions of the invention that are positioned adjacent to marine or land based wind turbines, use the sante grid connections and are used to smooth out power variations when the strength of the wind changes.

* Versions of the invention which incorporate a gas turbine to drive the circulation pump and use the gas turbine exhaust to provide the warm environment surrounding the heat engine according to the invention.

* Versions of the invention that are used as an alternative to solar panels for space craft and satellites.

Claims

<claim-text>Claims A turbine based heat engine that transfers energy from a moving working fluid to a set of turbine blades, allowing the turbine shaft to do external work, characterised by the engine operating at a higher efficiency than the maximum theoretical efficiency predicted by the Carnot equation by virtue of the fact that the engine extracts both sensible heat and bulk kinetic energy from the fluid.</claim-text> <claim-text>2, A heat engine according to the first claim, with the turbine being enclosed inside a closed loop conduit, with a circulation pump being added to drive the moving fluid through the turbine against the resistance of friction.</claim-text> <claim-text>3. A heat engine according to the first claim with the working fluid being a mixture of gases and vapours.</claim-text> <claim-text>4. A heat engine according to the first claim, with the turbine being enclosed inside a closed loop conduit, wit the conduit walls being thermally conducting so that heat from the environment can flow into the interior of the heat engine to re-warm the fluid alter it has done external work on the turbine.</claim-text> <claim-text>5. A heat engine according to the first claim, with the turbine being enclosed inside a closed loop conduit, with a circulation pump being added to drive the moving fluid through the turbine against the resistance of friction and a constriction being added in front of the turbine blades so that the fluid passes through the turbine blades at a higher mean speed than its mean speed when passing through the wider parts of the conduit.</claim-text> <claim-text>6. A heat engine according to the first claim, with thermally conducting, tapered centrally axial constrictions being placed immediately in front of and behind the turbine in order to increase the speed of the fluid transiting the turbine, with the constrictions having cavity walls and passage access to the external environment so that any gas, vapour or liquid in the external environment can flow though the cavities and transfer heat to the working fluid.</claim-text> <claim-text>7. A heat engine according to the first claim, with the turbine being enclosed inside a closed loop conduit, wit the conduit walls being thermally conducting so that heat from the environment can flow into the interior of the heat engine, with the environment including a sutured vapour that originates from a liquid that has been evaporated by the heat generated when an elastic fluid has been compressed.</claim-text> <claim-text>8. A heat engine according to the first claim, with the turbine being enclosed inside a closed loop conduit, wit the conduit walls being thermally conducting so that heat from the environment can flow into the interior of the heat engine, with the environment including a sutured vapour that originates from a liquid that has been evaporated by the heat supplied by indirect contact of the liquid with a hot fluid.</claim-text> <claim-text>9. A heat engine according to the first claim, with the turbine being enclosed inside a closed ioop conduit, wit the conduit walls being thermally conducting so that heat from the environment can flow into the interior of the heat engine, with the environment including a sutured vapour that originates from a liquid that has been evaporated by the heat supplied by indirect contact with the warm reservoir of a refrigerator.</claim-text> <claim-text>10. A heat engine according to the first claim, with the turbine being closely followed by a second turbine rotating in the opposite sense so that the angular momentum imparted to the working fluid as it passed through the gaps between the first set of rotating turbine blades is largely offset by the angular momentum imparted to the fluid as it passes through the gaps between the second set of turbine blades.</claim-text> <claim-text>11. A heat engine according to the first claim, with the circulation pump consisting of two sets of successive rotating irnpellor blades, with the two sets rotating in opposite senses, so that the working fluid has gained minimal angular momentum after passing though the circulation pump.</claim-text> <claim-text>12. A heat engine according to the first claim, with the circulation pump taking the form ofa jet pump which injects a stream of comparatively high speed fluid into the slower moving main body of the fluid, with thejet fluid originating as a fraction of the circulating fluid that has been drawn off and compressed prior to injection.</claim-text> <claim-text>13. A heat engine according to the first claim, with the engine being powered by waste heat produced during the amine carbon capture process.</claim-text> <claim-text>14, A heat engine according to the first claim, with the engine being powered by waste heat produced during a cryogenic carbon capture process.</claim-text> <claim-text>15. A heat engine according to the first claim, with the engine being powered by heat produced by nuclear fission reactions, with the nuclear reactor running at a sufficiently low temperature that it does not reach meltdown temperature if the reactor is left to cool by natural means following an emergency close down.</claim-text>