GB2565863A

GB2565863A - Turbine system

Info

Publication number: GB2565863A
Application number: GB1802729.2A
Authority: GB
Inventors: Pravinchandra Budhdeo Shamir
Original assignee: Engen House F Z C
Current assignee: Engen House F Z C
Priority date: 2017-08-23
Filing date: 2018-02-20
Publication date: 2019-02-27
Also published as: GB201802729D0; GB2565811A; GB201713565D0

Abstract

A closed system having a plurality of chambers 12 and a turbine 14. Each chamber has an inlet 16, an outlet 18, a plurality of heating elements (20, fig 3) and a plurality of cooling elements (22, fig 3). The outlets are connected by way of pipes 19, which may have pressure differential one-way valves 21, to the turbine inlet pipe 24, which preferably has a one-way valve 26 and a plurality of pressure differential one-way valves 27. Turbine outlet pipes 32 may lead back to the chambers 12.

Description

TURBINE SYSTEM

FIELD OF THE INVENTION

The present invention relates to turbines, more particularly carbon dioxide turbines. It is applicable for use with any carbon dioxide turbine, in particular those turbines which operate using the energy realised from carbon dioxide through sublimation.

BACKGROUND OF THE INVENTION

Current electricity turbines generally use water (steam) to provide the kinetic force to turn the blades of a typical prior art turbine to generate electricity. Water has been used as the medium of choice since the advent of the steam generator. Water is great for life due to its unique properties such as hydrogen bonding, but these very properties make it a poor and inefficient choice of a kinetic vector and transfer agent.

Water is a di-polar molecule. In essence, the hydrogen atoms of the water molecule are both located at one end of the molecule. This leaves the exposed nucleus and protons therein on one side and the heavy negative charge on the other. Consequently, water molecules attract one another in a phenomenon called hydrogen bonding. This effect requires a huge amount of energy to overcome in order to get water to convert to steam. Even in the vapour state, water molecules still weakly attract each other, hence the specific heat capacity is still quite high even in the vapour state.

Most fossil fuel electricity turbines work by heating water to superheated steam. This creates pressure across the blades of the turbine. The overall pressure applied and therefore the conversion efficiency is dictated by the pressure differential between the inlet and the outlet. Hence, in order to increase the pressure differential, the exit steam is rapidly condensed. The exit heat energy is therefore lost as the condensing liquid (normally water) absorbs the heat and is discharged. Extraction steam turbines and back process steam turbines both have a degree of cooling of outlet steam and this energy is wasted.

In simple terms, water (H₂O) has a specific heat capacity (SHC) of 4.2 KJ/Kg/K. So, water at 20^eC (room temperature) will require 80 Kelvin (K) equivalents of energy to increase the temperature of the water to 100^eC. It will then take 2260 KJ/KG to convert the liquid water to steam (latent heat of vaporisation). The steam is then superheated to an average 600 degrees Celsius. The SHC of steam is approximately 2.0 J/KG/K. Whilst much of the mechanical energy is converted to electrical energy (up to the theoretical maximum defined by Carnot’s Law at circa 60%), the overall efficiency of a turbine when considering the actual input energy (fossil fuel) is significantly lower.

From the prior art energy generation processes for low temperature heat utilization are known. These include so-called Organic Rankine Cycle (ORC) systems that work with evaporation media that evaporate down to 70 °C at 150 °C. Thus, waste heat, which as a process heat of less than 100 °C can still be converted to electricity.

For such circular processes the temperature difference between the evaporator side and the condenser side is essential for the efficiency of such a cycle plant. Modern ORC systems can run with an evaporator temperature of 70°C to 100°C and a condenser temperature of 30 °C to 40 °C. Therefore, the expected efficiency at a temperature difference of only 40 Kelvin is small and the prior art indicates that this is less than 10% for ORC systems.

Organic Refrigerant Cycle (ORC) Rankine Turbines work in a similar manner to steam turbines by applying a kinetic force to turbine blades. ORC Rankine Turbines work by taking liquid refrigerants and applying heat to them. Heat in such turbines is normally reclaimed waste heat and such turbines typically operate at 80 - 300^eC. The refrigerant absorbs latent heat to move phases from liquid to gas and the gas expands and creates pressure. This pressure is enhanced by accelerating the refrigerant molecules to create a force on the turbine blades. As the efficiency across a turbine is determined by the pressure differentials between input pressure and output pressure, the refrigerant is cooled rapidly by water and like the steam turbine, the latent heat of vaporisation is lost/wasted.

These turbines have an overall efficiency of 5-8% as opposed to 30 - 50% for steam turbines. However, as it is used for waste heat recovery, the cost of input fuel (oil/gas/coal) is mitigated. Hence, on a cost-benefit perspective, ORC Rankine Turbines are typically 33% more cost effective than a steam turbine.

As an alternative to using water to power electric turbines people have instead looked to use carbon dioxide. Carbon dioxide undergoes a process called sublimation to change directly from a solid to a gas without passing through a liquid phase. This physical change is a reversible reaction and releases and absorbs a fixed quantum of energy.

Carbon dioxide is a better choice of kinetic vector for turbines. It is a linear molecule with the oxygen atoms arranged on either side of the carbon atom. Hence it is more electrically neutral than water.

Carbon dioxide (CO₂) turbines use CO₂ gas and accelerate this gas to turn a standard turbine. The SHC of CO₂ is 0.8 KJ/Kg/K. Hence per given input of energy it accelerates 2.5 times as much as steam. Like all the turbines described above, efficiency is driven by cooling the outlet gas. CO₂ is normally taken to 300°C in a CO₂ turbine and the gas cooled to about 20°C. There is no latent heat to be lost but equally the pressure differentials are not sufficiently different and as such the overall efficiency is lower than that of a steam turbine.

US2008196208 (Klein) describes the use of solid carbon dioxide as a fuel source by using the sublimating properties of solid carbon dioxide to create pressure when it is contained which is then converted into mechanical energy (which in turn can then be turned into electrical energy) however, this patent does not except in very general terms how to put this into practice and how to obtain the best results from the sublimation process.

DE102011108970 (Interimo GMbH) describes power plant comprising a low temperature heat source and turbine which utilises waste heat which is at about 70°C. In this case carbon dioxide is cooled to a temperature of about -50°C before being subjected to waste heat at about 70°C which results in a pressure increase of about 3500 kPa which can then be used to operate the turbine. The problem with this system is that the heat being used whilst of low temperature compared with typical steam powered electricity plants is still significantly higher than the ambient waste heat found in homes and offices. This system fails to recover the phase change heat. In cooling to -50°C, the mechanical efficiency is enhanced, and this is slightly offset by the energy taken to cool the CO₂ down to -50°C. However, the energy, like cooling steam or refrigerant in an ORC Rankine Turbine, is ostensibly wasted.

JP2003126681 (TAKIGUCHI YOSHISUKE) describes the use of surplus or midnight (i.e.) cheap electricity to cryogenically freeze carbon dioxide which can then be stored or transported and then heated up at a later time or place to generate a pressurised gas to drive a turbine or motor. This system is a good small portable system but doesn’t look to maximise the amount of recoverable energy.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a carbon dioxide (CO₂) turbine system comprising a turbine and a plurality of chambers, each of the chambers having an inlet and an outlet, at least one heating element and at least one cooling element, wherein the outlets of the chambers are configured to feed CO₂into the turbine and the inlets of the chambers are configured to receive the CO₂ from the turbine.

One of the biggest advantages of the carbon dioxide turbine system of the present invention is the very high expansion pressure ratio and resultant increase in mechanical efficiency caused by the phase change due to the rapid solidification. This results in the pressure differential across the turbine being higher than that currently achieved by almost all prior art turbines. This is achieved by the negative pressure caused by the rapid phase change which results in volume reduction of about 860 times as the CO₂ freezes back to dry ice. This in turn forces a greater mechanical conversion which in turn also results in the input CO₂ gas cooling rapidly upon exit.

Preferably the system is a closed system.

Alternatively iodine, arsenic or naphthalene may be used instead of CO₂. However, these materials are difficult to handle, and are inefficient as compared to carbon dioxide.

Preferably the turbine has a single inlet and a plurality of outlets. This is advantageous as this acts to create a pressure differential across the turbine.

Preferably the turbine is provided with a plurality of blades. Preferably the CO₂ flows across the blades. Preferably the flow of CO₂ across the blades is drawn towards the plurality of outlets. This is because the plurality of outlets provides a greater area for the C0₂to exit from the turbine space.

Preferably the plurality of outlets are flared moving from a wider dimeter to a narrow diameter to provide the greatest area for exit from the turbine, and increase the velocity of flow back to the sublimation chambers.

Preferably the outlets of the chambers are configured to feed the CO₂ into the turbine through the single inlet.

Preferably the inlets of the chambers are configured to receive the CO₂from the turbine through a plurality of outlets.

Preferably the inlets of the chambers are flared moving from a narrow diameter to a wider diameter.

Preferably the outlets of the chambers are flared moving from a wider diameter to a narrow diameter.

Preferably the inlets of the chambers are configured to be connected to the turbine through at least one pipe.

Preferably the internal surface of the pipe is provided with a helical ridge, groove or other corrugation. This is advantageous as this encourages the acceleration of the CO₂through the pipe

Preferably the turbine is configured to be connected to the outlets of the chambers through at least one pipe. Preferably the pipe exits into the turbine.

Preferably the pipe is not insulated such that it is able to source additional heat from the surrounding area which in turn heats the gas in the pipe further which in turn accelerates the gaseous CO₂. The helical ridge, groove or other corrugation forms vortices within the pipe which further aids in the acceleration of the gaseous CO₂ through the pipe. Preferably the pipes progressively narrow causing pressure to increase along the pipe length.

Preferably the pipe has a series of valves installed along the length thereof. Preferably the valves are one way valves, more preferably pressure differential one way valves. Preferably the valves are spaced at a fixed volumes apart and increasing in pressure the pressure differential at which they open along the length of the pipe.

For example, the one-way pressure differential valve in the pipe closet to the chamber outlets, would open at a pressure differential of, for example, 1000 Psi. The next valve would be 10-20cm further along the pipe and would open at a pressure differential of, for example, 2000 Psi and so on. As the pressure differential valves are one way, the gas cannot travel backwards and more importantly unless the gas in the pipes does not exceed the next pressure differential valve it will not open. Accordingly, the fixed volume of space between any two valves will be provided with more CO2 which in turn will increase the pressure which will then exceed the next pressure differential valve. This allows the outlet pressure at the turbine to be controlled to the optimal entry pressure for the turbine as the last pressure differential valve will be at the entrance to the turbine.

Preferably the at least one heating element is configured as a capillary.

Preferably the at least one cooling element is configured as a capillary.

Preferably each of the chambers is provided with a plurality of heating elements.

Preferably each of the chambers is provided with a plurality of cooling elements.

Preferably the at least one heating element is a capillary tube provided with a heat exchange medium. Preferably the heat exchange medium is water. Preferably the heat exchange medium is configured to recover waste heat external to the system and transfer the heat into the system.

The carbon dioxide turbine system of the present invention is preferably to be used with low grade heat at 80°C derived from a heat pump. The heat pumps are a reverse refrigeration cycle and concentrate heat. The heat pumps could be ground source or airsource heat pumps for example. The heat from the heat pumps is transferred to water and this water is pumped into capillary tubes in a typically ovoid cylinder with two openings.

Capillary tubes are preferably provided as they offer the greatest surface area for heat exchange.

Preferably the at least one cooling element is a capillary tube provided with cryocooled medium. Preferably the cryocooled medium is liquid nitrogen or liquid helium. Preferably the cryocooled medium is configured to remove heat from the system.

Preferably the carbon dioxide turbine system is provided with a cryocooler. Preferably the at least one cooling element is connected to the cryocooler and the cryocooler cools the cryocooled medium.

The cryocooler causes the phase change in the CO₂ and in effect acts as a simple heat exchanger.

Preferably the at least one heating element is configured to operate at 55 to 60^eC.

Preferably the at least one cooling element is configured to operate at below -197^eC.

Preferably the at least one cooling element is configured to cool the CO₂ when it is present in the chamber in its gaseous form and cause the CO₂ to undergo sublimation and become solid.

Preferably the at least one heating element is configured to heat the CO₂ when it is present in the chamber in its solid form and cause the CO₂ to undergo sublimation and become gaseous.

Preferably the turbine volume is fixed depending on output of the turbine. A turbine may for example have a fixed volume of 100 litres which may require for example an inlet pressure of for example 6000psi. Preferably in order to achieve the required pressure CO₂is added or removed from the closed system, such that more or less CO₂ is available to enter the turbine.

Preferably exit of the CO₂ from the turbine is enhanced by the fact that the exit CO₂ is then condensed back to solid in an empty chamber using the cryocooler.

Preferably the flow rate of the cryocooled medium into the cooling capillary pipes causes the CO₂ to solidify rapidly. The condensation of the CO₂ into a solid reduces the exit volume of the gas by 860 times and this negative pressure differential causes the gaseous pressure differential across the turbine to further improve. In addition as the kinetic force of the CO₂ is more efficiently transferred, the exit CO₂ is cooler having converted its forward motion into mechanical energy. Therefore, the exit temperatures should be around -25°C or lower for CO2.

Preferably the CO₂ is condensed by a cryocooler and the energy of phase change which is normally wasted in prior art turbines is recovered by the cryocooled medium. Preferably the cryocooled medium absorbs the latent heat of condensation of the CO₂ and turns to gas in the last of nitrogen for example. Preferably the cryocooled medium is then cooled with pressure and changes back to a liquid. In doing so the cryocooled medium gives up its latent heat of condensation.

Preferably the cryocooler is encapsulated by a heat recovery box. Preferably the heat recovery box is filled with water or propylene glycol.

Preferably the latent heat of condensation passes into the air around the cryocooler which is encapsulated in a heat recovery box filled with water or propylene glycol for example. Preferably the heat recovery box keeps the closed cryocooler at ambient temperature. Preferably the latent heat of condensation is absorbed by a heat loop inside the heat recovery box and the heat is transferred to the heat pump to be reused in the operation of the turbine.

Preferably the heat given off by the cryocooler is recovered and since the system is closed loop no energy is wasted) except for the mechanical transmission losses envisaged by Carnot’s Theorem).

Thermodynamically, the efficiency of the system is far higher than anything currently available, not only through the sublimation/condensation process but also the recovery of phase change energy.

The system can be scaled up to any size and any sublimating material can be used. As with any closed system there will be some gas losses, and these are replaced in the turbine by using an atmospheric CO₂ condenser or using dry ice. The former is a better long-term engineering solution.

According to a second aspect of the present invention there is provided a method of generating electricity using the carbon dioxide turbine system described in relation to the first aspect of the present invention comprising the steps of:

a) providing a carbon dioxide (CO₂) turbine system comprising a turbine and a plurality of chambers, each of the chambers having an inlet and an outlet, at least one heating element and at least one cooling element, wherein the outlets of the chambers are configured to feed CO₂ into the turbine and the inlets of the chambers are configured to receive C0₂from the turbine;

b) introducing C0₂into the plurality of chambers, and preferably closing the system;

c) operating the at least one cooling element to cool the CO₂ whilst the CO₂ is present in the chamber in its gaseous form to cause the C0₂to undergo sublimation and become solid;

d) operating the at least one heating element to heat the CO₂ whilst the CO₂ is present in the chamber in its solid form to cause the CO₂ to undergo sublimation and become gaseous;

e) allowing the gaseous CO₂ to exit the chambers to feed into the turbine through the outlets;

f) receiving the gaseous CO₂ from the turbine into the chambers through the inlets;

g) repeating steps c) to f) as required.

Preferably the CO₂ in step b) is introduced and stored as a solid into the plurality of chambers. This is because the CO₂ occupies less volume for a given weight when solid.

Preferably step e) comprises opening a valve. More preferably step e) comprises opening a valve once the pressure of the gaseous CO₂ created in step d) reaches a pre-determined pressure. Preferably the pre-determined pressure is between about 70 bar (1015 Psi or 7000000 Pa) and about 130 bar (1885 Psi or 13000000 Pa).

Preferably in step e) the gaseous CO₂ exists the chamber through the outlet once the valve and travels through corrugated pipes which lead to the turbine.

For a given unit of energy (K), the carbon dioxide turbine of the present invention has the following advantages over current OCR Rankine Turbines

a) Closed loop self-contained turbine requiring no water cooling or external fossil fuel.

b) All energy (except mechanical losses) is utilised or re-absorbed, the latent heat of vaporisation is not lost as in steam or ORC Rankine Turbines.

c) The mechanical efficiency of the Rankine cycle is enhanced by the rapid condensation of the CO₂ to solid.

d) The turbine stores energy as a phase change battery with minimal losses as keeping the CO2 solid has an energy loss. This is recovered via the cryocooler and heat recovery box to be pushed back to re-usable energy via a heap pump loop and back into the turbine.

e) The differential valve system removes the need for a pump or mechanical energy loss in the system. The CO₂gas expands, and the differential valves ensure that the CO₂ inlet pressure is delivered without using any pumps.

f) Capillary tubes offer the greatest surface area for heat transfer into the CO₂ and for liquid nitrogen or other cryocooled medium to absorb the latent heat of condensation.

g) The chambers act as both expansion chambers and condensation chambers in sequence.

h) The only moving parts are the pumps in the cryocooler, the valves, the turbine blades and the electrical generator apparatus.

i) The mechanical efficiency is higher than any CO₂ turbine and overall efficiency when including input energy is the highest of any Rankine turbine.

j) The carbon dioxide turbine of the present invention is the only system that uses the expansion ratio of CO₂ in the phase change from solid to gas to produce the pressures, which is far greater than using super-critical CO₂ turbines.

k) The carbon dioxide turbine of the present invention is the only system that causes rapid contraction with a helium/nitrogen cryocooler which increases the efficiency of the turbine to over 55% compared to 15% for a typical CO₂ turbine. It does this by causing a contraction of the CO₂ by 860 times which then causes a negative pressure on the outlet. No other CO₂ turbine does this. Steam turbines do by cooling the steam but they lose the latent heat of condensation. The rate of cooling in the carbon dioxide turbine of the present invention is far higher than any steam turbine.

l) The carbon dioxide turbine of the present invention is the only system that absorbs the latent heat of condensation from the nitrogen or helium cryocooler. The closed loop system has an overall energy conversion per unit of energy used of approximately 80% as losses are only the mechanical losses in the turbine and any radiant losses in the Heat pump and heat recovery cycles.

m) Unlike steam turbines or even ORC Rankine Turbines, no water supply is required.

n) The carbon dioxide turbine of the present invention also acts as a high efficiency battery as the biggest losses in keeping the CO₂ solid is the heat ingress which is absorbed via the cryocooler and reabsorbed for mechanical use.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Figure 1 illustrates a schematic view of the turbine system of the present invention;

Figure 2 illustrates a schematic view of the turbine system of the present invention with additional solar thermal collectors;

Figure 3 illustrates a view of a chamber of the turbine system; and

Figure 4 illustrates a cut away view of a section of the pipe.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As set out above current electricity turbines generally use water (steam) to provide the kinetic force to turn the blades on a typical prior art turbine to generate electricity. Water has been used as the medium of choice since the advent of the steam generator. Water is great for life due to its unique properties such as hydrogen bonding, but these very properties make it a poor and inefficient choice of a kinetic vector and transfer agent.

In order to use water to power a typical prior art turbine we first need to heat the water to 100°C to convert the water to steam.

The Energy required for boiling water (molecular mass) to steam per kg is as follows:

100 x Specific Heat Capacity of water + Latent Heat of Vaporisation.

100 X 4.2 = 420KJ + 2260KJ = 2680KJ to heat 1 kg of water to 100°C.

In order to power a typical prior art turbine, however, steam itself is not good enough and the steam needs to be superheated to 192°C.

(192- 100) x 2.1 (SHC of steam) = 92 x 2.1 = 193.2KJ.

Therefore, the total energy required to super heat 1 kg of water to 192°C = 2680 + 193.2 = 2873.2KJ.

When steam is superheated to 192°C this is able to generate a force equivalent to 83 PSI (572265 Pa) to power the typical prior art turbine.

However, in order to generate the maximum pressure differential across the turbine blades, the volume of steam is dramatically reduced by condensing the steam.

This means that latent heat of vaporisation is given up for each 1 kg of the steam to obtain 83psi (572265 Pa) of force. Therefore, the amount of energy per PSI is 83/ (2260 + 93) = 28.34KJ/PSI (0.00411 KJ/Pa). It is also worth noting that steam has an expansion ratio of 1600.

The inefficiency of steam arises from the lost energy in vaporisation which is not reclaimed in condensation. This is separate to any of the energy losses that may occur in the turbine itself.

As an alternative to using water to power electric turbines people have instead looked to use carbon dioxide (CO₂). CO₂ undergoes a process called sublimation to change directly from a solid to a gas without passing through a liquid phase. This physical change is a reversible reaction and releases and absorbs a fixed quantum of energy.

CO₂ is a better choice of kinetic vector for turbines. It is a linear molecule with the oxygen atoms arranged on either side of the carbon atom. Hence it is more electrically neutral than water.

CO₂ sublimates at -78°C (194 Kelvin (K) approximately) and it has an expansion ratio of 845 and 1 kg of Dry Ice (solid CO₂) occupies 0.666 litres in volume.

The SHC of CO₂ is 0.82KJ/Kg which is less than that of water and its molecular mass is 44 which is greater than that of water which is important as a greater mass is capable of creating a greater force (F=M x A).

The amount of energy required to produce a given increase in temperature and force is described by the SHC of a substance. In a gas or a liquid, the movement of molecules or atoms is a measure of temperature. The forward kinetic motion of a substance is key to turbine efficiency.

Steam has a SHC of 2.1 KJ/Kg/K whereas CO₂ has a SHC of 0.82KJ/Kg/K. Hence for a given amount of energy supplied (amount of increase in temperature), CO₂ will have over double the kinetic energy of steam. The amount of force applied per given acceleration is higher in CO2 than water. Since CO2 is heavier than water in terms of molecular weight the Specific Heat Capacity is therefore four times that of steam since a one Kelvin equivalent of energy results in a higher translational force for a heavier molecule.

Furthermore, using the equation F=M x A, it follows that for a given acceleration CO₂ has a greater mass and therefore will exert a greater force on the turbine blades.

In summary, CO₂ takes less energy to accelerate and has a greater force on turbine blades than steam. As discussed above, a one Kelvin equivalent of energy will result in a fourfold increase in force compared to steam.

Calculation for 1 Kg of CO₂ at 55°C that is 328K at a volume of 10 L is shown below.

PV = nRT is the gas equation.

Pressure = 227 x 0.0821 x 328/10 = 611.28 atm = 8983.339 Psi (61937942.086 Pa) per 10 kg of CO₂.

The efficiency of a turbine is limited by Carnot’s Theorem. 60% is considered to be an excellent efficiency. The efficiency of a turbine is affected by the energy losses in converting heat energy to mechanical energy and from this into electricity.

Looking now to the specifics of the present invention.

Figure 1 illustrates a first embodiment of the present invention. The system 10 generally comprises a plurality of chambers 12, and a turbine 14. Each of the chambers 12 having an inlet 16, an outlet 18, a plurality of heating elements 20 and a plurality of cooling elements 22 which are shown in more detail in Figure 3. The outlet 18 of each of the chambers 12 being connected through pipes 19 provided with pressure differential one way valves 21 to a turbine inlet pipe 24 provided with a one-way valve 26 and a plurality of pressure differential one way valves 27. The turbine inlet pipe 24 being configured to connect to the turbine 14. The turbine 14 being provided with a plurality of blades 29 a drive shaft 28 and an electrical generation means 30 such as an electricity generator. The turbine 14 also comprises a plurality of turbine outlet pipes 32, one for each chamber 12 provided. In an alternative only one main turbine outlet pipe could be provided which then splits into a plurality of pipes for each chamber provided. Each turbine outlet pipe 24 in the embodiment illustrated then connects with the respective inlet 16 of the respective chamber 12.

A suitable turbine for use in the present invention is a Siemens SST 060 turbine which has a range of 2MW to 6MW with an operating pressure of up to 1900 Psi (13100000 Pa) for a 6MW production.

However, the particular turbine or blades used in the present invention can be the same as those used in any conventional steam turbine.

In order to operate this turbine using CO₂ (assuming a 60% efficiency) a constant volume of 120 kg of solid CO₂ is required to be vaporised and fed into the system, the system to include the volume of pipe work, the expansion chamber within the turbine, the exhaust pipes and storage cylinders.

The amount of CO₂ required will vary for different turbines. The final volumes and metric are dependent upon variable factors such as type of turbine blades, expansion chamber and exhaust sublimate cylinders. The amount of CO₂ within the sealed unit is dependent upon the turbine and the heat source applied.

Based on the power requirement, and the pressure of gas needed to turn the turbine to produce the required speed, the amount of CO₂ is chosen. This once again goes back to the ideal gas equation. A certain amount of solid CO₂ confined in a certain volume produces a certain gas pressure upon sublimation. This is also a trade-off between the amount of CO₂ gas, the size of the bulb shaped sublimation chambers and the number of chambers. This pressure energy drives the turbine at a certain speed.

The system of the present invention moves away from using water as the kinetic vector and instead solid CO₂ is used in a sealed turbine unit.

The system operates on a cyclical cylinder rotation basis. The general process is that a volume of gaseous CO₂ is solidified rapidly, preferably by using a cryocooler and whilst at the same another volume of solidified CO₂ is exposed to 55 to 60°C a heat exchange medium such as water to convert previously solidified CO₂back into a gas and in doing so expand its volume.

Liquid nitrogen is obtained by cooling N₂ gas to 77K or -196°C. Nitrogen gas is extracted from the atmosphere in air separation plants using membrane units and then liquefied, or air can be first liquefied and liquid nitrogen can be extracted from it using fractional distillation. Since nitrogen gas is available freely (78%) in the atmosphere, liquid nitrogen is an ideal substance to use as compared to liquid helium. Cryocoolers are basically refrigerators that can cool a substance down to extremely low cryogenic temperatures. The simplest ones are Stirling cryocoolers which are can be purchased from manufacturers in the UK such as SHI, Oxford Cryosystems and Cryogenic Limited. The liquid nitrogen produced by these coolers is stored in suitable cryogenic tanks to be used when required. The tanks can be suitably connected to the capillary tubes which are introduced into the bulb-shaped chambers of the turbine and the liquid nitrogen can be transferred via a pump.

In the example set out each of the chambers 12 has a volume of 10 litres and are each capable of containing 10 kg (6.66 litres) of solid CO₂. As the heat exchange medium passes through the heating elements 20 during the heating cycle of the chamber 12 the solid CO₂ will sublime into a gas and will result in the volume of CO₂ in the chamber 12 expanding. An outlet pressure valve (not shown) on the chamber 12 would prevent release of the gaseous CO₂ until a given pre-set pressure is reached, which in the present example would be around 1300 Psi (8963184 Pa). The outlet pressure valve would then open and release the CO₂, and close again once all the CO₂ has been released ready for the next cycle. In addition the CO₂ cylinder’s inlet valve (not shown) would open ready to receive exhaust CO₂, as discussed in more detail below. The heat exchange medium would then cease to flow into heating elements 20 in that chamber 12 and would move to flow into the heating elements 20 in the next chamber 12 in the sequence.

Each chamber 12 comprises inlets 16 and outlets 18 as shown in more detail in Figure 3. Each of the inlets and outlets 16, 18 are provided with a conical funnel having helical ridges/grooves. This conical shape with helical ridges/grooves, causes the expanded gaseous CO₂ to accelerate on entrance to or exit from the chamber 12. The helical ridges/grooves increase the vortex effect which in turn increases acceleration of the gaseous CO₂. The pipes 19, 24, 32 leading to and from the turbine chamber are also provided with helical ridges/grooves to continue the acceleration of the gaseous CO₂.

The number and volume of chambers 12 which need to be heated at a given time depends of the pressure of gaseous CO₂ required by the turbine to generate the required electrical output from the turbine. The greater the demand (i.e. required electrical output from the turbine), the greater the number of chambers 12 that need to be heated at a given time, which results in a greater kinetic force being applied to the blades 29 of the turbine.

The efficiency of the turbine 14 is heavily dependent on the pressure differential across the entrance and exit of the turbine blades 29. To assist in this, the turbine 14 preferably has only one inlet 25 to maximise the inlet force and multiple outlets 31 and outlet pipes 32 for the exhaust CO₂ to flow into multiple chambers 12 since the greater the exhaust area, the lower the pressure at exit. The inlet pipe 25 is arranged to create a laminar flow across the blades 29 of the turbine 14. This is different to many modern turbines which are provided with a few inlet pipes and a static blade to force air flow across the rotational blades behind the fixed blades, which results in an increase in air resistance which in turn reduces mechanical force.

In order to further maximise the inlet force not only is preferably only a single inlet 25 provided, but that the diameter of the inlet pipe 24 reduces in diameter as it approaches the inlet 25.

In addition as described above both the inlet pipe 24 and the outlet pipes 32 are provided with internal helical ridges/groves which result in forward linear vortexing of the CO₂ gas flowing there through. A cut away section of a portion of a pipe illustrating this is shown in Figure 4. The speed of the gas is increased by forcing the CO₂ gas to swirl at the edges of the flow. This increases the velocity of the CO₂ gas on the outside of the flow and decreases the turbulence of the CO₂ gas in the centre of the pipe. The purpose of the internal helical ridges/groves are to force this vortexing which in turn increases the flow rates of the CO₂ gas. This means that the inlet flow rate is higher and the exit flow rate is lower resulting in a greater differential.

In addition to providing multiple outlets 31 and outlet pipes 32 for the exhaust CO₂ to leave the turbine 14 the outlets 31 that lead to the exit pipes 32 are flared, like a trumpet with a larger inlet. Preferably there are 4 times more outlets 31 and outlet pipes 32 compared to the number of inlet pipes 25, more preferably 8 times more outlets 31 and outlet pipes 32 compared to the number of inlet pipes 25.

The outlet pipes 32 gradually increase in diameter as they move from their flared exits 27 from the turbine 14 to the inlets 16 of the chambers 12 as illustrated in Figure 1. The inlets 16 of the chambers 12 are also flared in the opposite direction to the flaring of the exits such that the inlet widens rapidly. This allows the gas to expand across the chamber 12 of the chamber rapidly. The chamber 12 ellipsoidal in shape like a bulb or a pear. The shape of the chamber 12 is such that it creates the maximum exit force when the heated gaseous CO₂ is allowed to exit the chamber 12. The chamber 12 is a double walled vacuum chamber having a flared inlet 16 and a flared outlet 18, the flared outlet 18 being flared in the opposite direction to the inlet 16. The flared inlet 16 provides a large exit area for the gaseous CO₂ leaving the turbine 14. The gaseous CO₂ will rapidly fill the chamber and come into contact with the cooling elements 22 extending into the internal volume 21 of chamber 12, which will cool the gaseous CO₂ and cause it to become solid. The lower the exit pressure of the gaseous CO₂ from the turbine 14, the lower the exit temperature of the CO₂, and thus less energy is require to cool the gaseous CO₂ to form the solid CO₂.

In addition to provide the greatest differential, the exhaust pipes 32 lead to chambers 12 that are being cooled using a cryocooler 34 such as a nitrogen cryocooler. In Figure 1, the cryocooler 34 is cooling the exhaust CO₂ gas in the chambers 12 using the cooling elements 22 which results in the CO₂ solidifying and contracting by around 860 times its gaseous volume. The faster the contraction, the greater the negative pressure or pressure differential across the turbine 14, and the more efficient the turbine 14 is.

The cooling elements 22 and the heating elements 20 are designed using organic biological ideas such as seen in capillaries in the skin. The cooling elements 22 and the heating elements 20 extend into the internal volume 21 of chamber 12 in a capillary design as shown in Figure 2. This provides the greatest surface area for the CO₂ to be exposed to either the heat change medium or the cryocooled medium for the transfer of the heat as quickly and efficiently as possible.

The heating elements 20 and cooling elements 22 are arranged in the chambers 12 extending internally in the internal volume 23 of the chambers 12. The heating elements and cooling elements 22 comprise small pipes forming capillaries. The pipes are configured in the case of the heating elements 20 to carry the heat exchange medium from heat exchanger 35 into chamber 12 to heat up solid CO₂, and in the case of the cooling elements 22 to carry cryocooled medium such as cryocooled liquid nitrogen or cryocooled liquid helium from cryocooler 34 into chamber 12 to cool gaseous CO₂ to solidify it.

The heating elements 20 and cooling elements 22 should be arranged alternately and generally uniformly in the chambers 12. However, preferably the heating elements 20 should not be present around the inlet 16 to the chamber 12 and the cooling elements 22 should not be present around the outlet 18 of the chamber 12.

In the case of cryocooled liquid nitrogen it will have temperature below -197^eC (as that is the boiling point of nitrogen), which when it passes through the cooling elements 22 will cool the CO₂ rapidly, which in turn will result in a rapid contraction in the volume of the CO₂in the chamber 12 which will create a negative pressure gradient and in turn draw more CO2 into the chamber 12 from the turbine 14.

As mentioned above it is also possible to use cryocooled liquid helium, however the commercial availability of liquid nitrogen makes nitrogen the initial preferred choice. Helium has a higher specific heat capacity than nitrogen, which means it can cool using a smaller volume. It would take 5 times the mass of liquid nitrogen to produce a 1^eC reduction in temperature compared to mass of liquid helium required for the same reduction.

In the example described once 7 litres of gas has passed into the chamber 12, the CO₂cylinder’s inlet valve (not shown) will close and the exhaust CO₂ will flow into the next chamber in the sequence to be cooled.

This system is designed to provide the greatest pressure differential across the turbine 14 and provide an efficiency above those in steam or diesel turbines and current CO₂systems.

Whilst electricity will be used to cryocool the cryocooled medium (liquid nitrogen/helium or other suitable medium), the heat obtained and used in the heat exchange medium should be recovered heat in order to operate the turbine 14 with a net electrical gain. Recovered heat includes heat obtained through heat exchange with ambient heat such as that from electrical appliances and waste warm water used in baths and sinks as well as geothermal and thermodynamic energy harvesters.

The flow rate of the cryocooled medium into the cooling capillary pipes causes the CO₂ to solidify rapidly. The condensation of the CO₂ into a solid reduces the exit volume of the gas by 860 times and this negative pressure differential causes the gaseous pressure differential across the turbine to further improve. In addition as the kinetic force of the CO₂is more efficiently transferred, the exit CO₂ is cooler having converted its forward motion into mechanical energy. Therefore, the exit temperatures should be around -25°C or lower for CO₂.

The CO₂ is condensed by a cryocooler and the energy of phase change which is normally wasted in prior art turbines is recovered by the cryocooled medium. The cryocooled medium absorbs the latent heat of condensation of the CO₂and turns to gas in the last of nitrogen for example. The cryocooled medium is then cooled with pressure and changes back to a liquid. In doing so the cryocooled medium gives up its latent heat of condensation.

The cryocooler 34 is encapsulated by a heat recovery box 36. The heat recovery box is filled with water or propylene glycol.

The latent heat of condensation passes into the air 37 around the cryocooler 34 which is encapsulated in a heat recovery box 37 filled with water or propylene glycol for example. The heat recovery box 37 keeps the closed cryocooler 34 at ambient temperature. The latent heat of condensation is absorbed by a heat loop inside the heat recovery box 34 and the heat is transferred to the heat pump to be reused in the operation of the turbine.

The heat given off by the cryocooler is recovered and since the system is closed loop no energy is wasted) except for the mechanical transmission losses envisaged by Carnot’s Theorem).

The carbon dioxide turbine system of the present invention is generally to be used with a heat exchanger 35 which obtains low grade heat at 80°C derived from a heat pump. The heat pumps are a reverse refrigeration cycle and concentrate heat. The heat pumps could be ground source or air-source heat pumps for example. The heat from the heat pumps is transferred to the heat exchange medium.

In an alternative instead of using recovered heat, instead heat may be obtained from the environment such as by using solar thermal collectors 40 as illustrated in Figure 2 to collect heat generated from the sun or through the use of air or ground source heat pumps and heat exchangers. In Figure 2 like parts are given like references numbers from Figure 1. In geothermal applications for example an outlet fluid from a deep geothermal borehole would be passed through a heat exchanger which would be used to raise the temperature of heat exchange medium in the heat exchanger to 55 to 60°C (333 Kelvin). The heat exchange medium would then pass to the chambers 12 and through the plurality of heating elements 20 in chambers 12 during the heating cycle.

The biggest failing in geothermal heat uptake has been the transmission of the energy obtained from the ground. Currently geothermal heat is used in district heating systems. Heat losses over distance makes transmission of heat over large distances expensive and impractical and would require major investment in thermally insulated pipping networks. However, the CO₂ turbine allows the geothermal heat to be converted to electricity and transmitted using existing infrastructure.

Typically 12 x 600m boreholes would provide sufficient energy to power a 6MW turbine. The deeper the borehole, the greater the heat.

Further in the alternative whilst not creating a net electrical gain but a net costs gain it would be possible to using cheap night rate electric to operate the cryocooler to store the energy in the solid CO₂ and use a smaller amount of more expensive day rate electric to heat up the heat exchange medium to operate the turbine 14 during the day. This would also operate a as battery to store the energy.

The sublimation of CO₂ is a reversible physical reaction and solid CO₂ provides a source of potential energy. The more CO₂ that is solidified by the cryocooler, the more energy is stored for release later. The amount of potential energy stored and available for release is directly dependent upon the volume of CO₂ available, the size of the cryocooler and the size of the turbine being used to release the energy. In effect, the process is like creating a battery.

All electricity turbines work on the principle of using a medium to create a kinetic force which turns a fixed magnet inside an electromagnetic coil creating electricity. There are AC and DC turbines but in the main, a pressurised gas is forced across fixed blades which cause lift and rotational forces. The efficiency of the turbine is affected by the differential of pressure across the blades. The higher the inlet pressure and lower the outlet pressure, the greater the flow rate of gas across the blades. This increase in flow rate results in greater lift and rotational force.

The key differential in the CO₂ turbine design is in the condensing cycle and the reduction of pressure across the turbine fan.

In the system of the present invention as illustrated in both Figures 1 and 2, the entire system is a self-contained closed loop turbine system 10. The inlet pressure is directly proportional to the volume of CO₂ in the closed system and the heat energy applied to the CO₂ contained in the system.

Claims

1. A carbon dioxide (CO2) turbine system comprising a turbine and a plurality of chambers, each of the chambers having an inlet and an outlet, at least one heating element and at least one cooling element, wherein the outlets of the chambers are configured to feed CO2 into the turbine and the inlets of the chambers are configured to receive the CO2 from the turbine.

2. A carbon dioxide (CO2) turbine system as claimed in claim 1 wherein the system is a closed system.

3. A carbon dioxide (CO2) turbine system as claimed in claim 1 or claim 2 wherein the turbine has a single inlet and a plurality of outlets.

4. A carbon dioxide (CO2) turbine system as claimed in claim 3 wherein the turbine is provided with a plurality of blades.

5. A carbon dioxide (CO2) turbine system as claimed in claim 4 wherein the CO2flows across the blades.

6. A carbon dioxide (CO2) turbine system as claimed in claim 5 wherein the flow of CO2 across the blades is drawn towards the plurality of outlets.

7. A carbon dioxide (CO2) turbine system as claimed in any of claims 3 to 6 wherein the plurality of outlets are flared moving from a wider dimeter to a narrow diameter.

8. A carbon dioxide (CO2) turbine system as claimed in any of claims 3 to 7 wherein the outlets of the chambers are configured to feed the CO2 into the turbine through the single inlet.

9. A carbon dioxide (CO2) turbine system as claimed in any of claims 3 to 8 wherein the inlets of the chambers are configured to receive the C02from the turbine through a plurality of outlets.

10. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the inlets of the chambers are flared moving from a narrow diameter to a wider diameter.

11. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the outlets of the chambers are flared moving from a wider diameter to a narrow diameter.

12. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the inlets of the chambers are configured to be connected to the turbine through at least one pipe.

13. A carbon dioxide (CO2) turbine system as claimed in claim 12 wherein the internal surface of the pipe is provided with a helical ridge, groove or other corrugation.

14. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the turbine is configured to be connected to the outlets of the chambers through at least one pipe.

15. A carbon dioxide (CO2) turbine system as claimed claim 14 wherein the pipe exits into the turbine.

16. A carbon dioxide (CO2) turbine system as claimed in claim 14 or claim 15 wherein the internal surface of the pipe is provided with a helical ridge, groove or other corrugation.

17. A carbon dioxide (CO2) turbine system as claimed in any of claims 14 to 16 wherein the pipe is not insulated such that it is able to source additional heat from the surrounding area.

18. A carbon dioxide (CO2) turbine system as claimed in any of claims 14 to 16 wherein the pipe progressively narrows.

19. A carbon dioxide (CO2) turbine system as claimed in any of claims 14 to 16 wherein the pipe has a series of valves installed along the length thereof.

20. A carbon dioxide (CO2) turbine system as claimed in claim 19 wherein the valves are one way valves.

21. A carbon dioxide (CO2) turbine system as claimed in claim 19 wherein the valves are pressure differential one way valves.

22. A carbon dioxide (CO2) turbine system as claimed in claim 19 wherein the valves are spaced at a fixed volumes apart and increasing in pressure the pressure differential at which they open along the length of the pipe.

23. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one heating element is configured as a capillary.

24. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one cooling element is configured as a capillary.

25. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein each of the chambers is provided with a plurality of heating elements.

26. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein each of the chambers is provided with a plurality of cooling elements.

27. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one heating element is a capillary tube provided with a heat exchange medium.

28. A carbon dioxide (CO2) turbine system as claimed in acclaim 27 wherein the heat exchange medium is water.

29. A carbon dioxide (CO2) turbine system as claimed in claim 27 or claim 28 wherein the heat exchange medium is configured to recover waste heat external to the system and transfer the heat into the system.

30. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one cooling element is a capillary tube provided with cryocooled medium.

31. A carbon dioxide (CO2) turbine system as claimed in claim 30 wherein the cryocooled medium is liquid nitrogen or liquid helium.

32. A carbon dioxide (CO2) turbine system as claimed in claim 30 or claim 31 wherein the cryocooled medium is configured to remove heat from the system.

33. A carbon dioxide (CO2) turbine system as claimed in further comprising a cryocooler.

34. A carbon dioxide (CO2) turbine system as claimed in claim 33 when dependent on claim 30 wherein the at least one cooling element is connected to the cryocooler and the cryocooler cools the cryocooled medium.

35. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one heating element is configured to operate at 55 to 60eC.

36. A carbon dioxide (CO2) turbine system as claimed in wherein the at least one cooling element is configured to operate at below -197eC.

37. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one cooling element is configured to cool the CO2 when it is present in the chamber in its gaseous form and cause the CO2 to undergo sublimation and become solid.

38. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the at least one heating element is configured to heat the CO2 when it is present in the chamber in its solid form and cause the CO2 to undergo sublimation and become gaseous.

39. A carbon dioxide (CO2) turbine system as claimed in any preceding claim wherein the turbine volume is fixed depending on output of the turbine.

40. A method of generating electricity using the carbon dioxide turbine system comprising the steps of:

a) providing a carbon dioxide (CO2) turbine system as claimed in any of claims 1 to 39;

b) introducing C02into the plurality of chambers, and preferably closing the system;

c) operating the at least one cooling element to cool the CO2 whilst the CO2 is present in the chamber in its gaseous form to cause the CO2 to undergo sublimation and become solid;

d) operating the at least one heating element to heat the CO2 whilst the CO2 is present in the chamber in its solid form to cause the CO2 to undergo sublimation and become gaseous;

e) allowing the gaseous CO2 to exit the chambers to feed into the turbine through the outlets;

f) receiving the gaseous CO2 from the turbine into the chambers through the inlets;

g) repeating steps c) to f) as required.

41. A method as claimed in claim 40 wherein the CO2 in step b) is introduced and stored as a solid into the plurality of chambers.

42. A method as claimed in claim 40 or claim 41 wherein step e) comprises opening a valve.

43. A method as claimed in claim 40 or claim 41 wherein step e) comprises opening a valve once the pressure of the gaseous CO2 created in step d) reaches a pre-determined pressure.

44. A method as claimed in claim 43 wherein the pre-determined pressure is between about 70 bar (1015 Psi or 7000000 Pa) and about 130 bar (1885 Psi or 13000000 Pa).

45. A method as claimed in claim 43 wherein in step e) the gaseous CO2 exists the chamber through the outlet once the valve and travels through corrugated pipes which lead to the turbine.