Apparatus and method of energy recovery for use in a power generating system using the Venturi effect

Abstract

This invention relates to a method of condensing and energy recovery within a thermal power plant using the Venturi effect and gas stored under hydrostatic pressure and to an energy storage system using the method in a hydrogen and oxygen combusting turbine, where the hydrogen and oxygen gasses are produced by water electrolysis and hydrostatically pressurized and stored.

Claims

1. A method of energy recovery for a thermal power plant, said method comprising the following steps: (a) a first working fluid delivering energy to a main power generating turbine then passes through a heat exchanger means in a Venturi condenser whereupon at least some of the energy remaining is extracted, and at least some of the first working fluid condenses to a liquid state; (b) a second working fluid enters one or more Venturi tubes in the Venturi condenser at elevated pressure, the second working fluid cooling and decreasing in pressure as it passes through the one or more Venturi tubes the second working fluid absorbing thermal energy from the first working fluid in the heat exchanger means in the Venturi condenser; (c) a reduced volume of the first working fluid causing a decreased pressure downstream of the main power generating turbine which increases flow of the first working fluid through the main power generating turbine; (d) the second working fluid after absorbing thermal energy in the heat exchanger means passing through a second power generating turbine where energy is extracted.

2. The method of energy recovery according to claim 1 wherein the second working fluid, ducted through the Venturi condenser during periods of higher electricity demand to provide condensing and energy recovery, is compressed using off peak or lower demand energy it for storage under hydrostatic pressure for release on demand.

3. The method of energy recovery according to claim 1 in which hydrogen and oxygen gasses are produced by a method of water electrolysis, the gasses are stored under hydrostatic pressure, are introduced into and combusted in a gas turbine, the combustion producing the first working fluid which is condensed using the Venturi condenser.

4. The method of energy recovery according to claim 2 wherein storage units are located within an adapted deep mine or part of an adapted deep mine and the hydrostatic pressure is derived from a mineshaft.

5. The method of energy recovery according to claim 3 wherein storage units are located within an adapted deep mine or part of an adapted deep mine and the hydrostatic pressure is derived from a mineshaft.

6. A power generating system comprising a thermal power plant including: (a) a vaporiser means for vaporising a first working fluid, a conduit means for conducting said (vaporised) first working fluid to a main power generating turbine for extracting energy from the first working fluid; (b) conduit means for taking the first working fluid exiting the main power turbine to a Venturi condenser, the first working fluid passing through heat exchanger means in the Venturi condenser to transfer heat to a second working fluid; (c) the Venturi condenser, provided with an inlet for receiving the second working fluid at elevated pressure, an inlet leading to one or more Venturi tubes, the one or more Venturi tubes having a converging inlet portion, a straight constricted portion and a diverging outlet portion, a further heat exchanger means surrounding the diverging outlet portion; (d) a second power turbine for extracting energy from the second working fluid exiting the one or more Venturi tubes; (e) conduit means for returning said first working fluid to the vaporising means; (f) pumping means for pressurising and returning said first working fluid to the vaporising means; (g) pump means for optionally pumping the second working fluid to a hydrostatically pressurised storage unit; (h) storage means for storing said second working fluid in gaseous state under hydrostatic pressure; and (i) conduit means for conducting the second working fluid from said storage means to the inlet of the Venturi condenser.

7. The power generating system according to claim 6 further including an electrolysis system for electrolysing water to produce hydrogen and oxygen gasses.

8. The power generating system according to claim 7 in which said second working fluid includes oxygen produced by the electrolysis system and released from the storage means for storing said oxygen gas under pressure.

9. The power generating system according to claim 6 in which the Venturi condenser has a plurality of Venturi tubes arranged to operate in parallel.

10. The power generating system according to claim 6 in which the Venturi condenser has a plurality of Venturi tubes arranged to operate in series.

11. The power generating system according to claim 9 in which the Venturi condenser includes the heat exchanger and/or the further heat exchanger means arranged to interact with the plurality of Venturi tubes to transfer heat from the first working fluid to the second working fluid.

Description

BRIEF DESCRIPTION

(1) FIG. 1 shows a schematic representation of a Venturi condenser within a thermal power plant with a hydrostatically pressurised stored gas flow;

(2) FIG. 2 shows a schematic diagram of a hydrogen oxygen electrolysis and gas turbine generation system with hydrostatically pressurised fuel, oxygen, and air storage;

(3) FIG. 3 shows an example configuration of a hydrogen oxygen electrolysis and compressed air system within a former coal mine;

(4) FIG. 4 shows an example of a configuration in which the Venturi Condenser has two Venturi tubes operating in a parallel mode;

(5) FIG. 5a shows an example of a multiple stage decompression in which the working fluid flows through two sections of a Venturi tube which each enable partial decompression. FIG. 5b shows a diagram of the variation of temperature and pressure along the Venturi tube.

DETAILED DESCRIPTION

(6) The following embodiments are shown by way of example only. More complex arrangements may be preferred which will be further embodiments of this invention. By way of example such embodiments may include any turbine generating arrangement which includes the condensing mechanism as shown, a plurality or combined use of any of the components shown, or additional components which supplement the components and methodology shown. Examples of additional components are parallel gas flows and fins on the tubular sections within the Venturi condenser, electrical control and ancillary equipment, and various valves and nozzles to control, adjust, or maintain the gas flow. The working fluid to be condensed is typically steam, and the gas used to condense that working fluid is typically air, or parallel flows of air and pure oxygen, although other working fluids and or gasses might be used where appropriate.

(7) Referring to FIG. 1, there is shown a schematic diagram of a system in which a hydrostatically powered condenser using the Venturi effect extracts energy from a thermal power plant turbine. During energy extraction, the exhausted steam or other first working fluid (1) enters a condenser (6) in a slightly superheated or saturated state, as much of the useful energy has already been extracted during expansion through a first turbine (2). A significant proportion of energy remains in the first working fluid (1) at this stage due to its latent heat of vaporisation which cannot be recovered in the turbine. Some or all of this energy is extracted by a second working fluid in gaseous form (3) which is forced under hydrostatic pressure through the condenser via at least one ducted pipe arrangement in the form of a Venturi tube. This second working fluid gas passes through a restricted section of the Venturi tube at or within the condenser. The Venturi tube comprises, in known manner, at least one converging (4) and diverging (5) sub-sections and one narrowed straight section between each converging and or diverging sections. As the second working fluid gas passes through (4), its pressure drops and is converted into velocity, which effect reduces its temperature allowing significant heat absorption from the first working fluid. As the second working fluid extracts thermal energy from the first working fluid which is exhausted from the first turbine (2), this causes a phase change from gas to liquid and consequently a volume reduction in that fluid, creating a lower pressure within the condenser (6) and consequently encouraging and enhancing flow through the turbine (2). When the second working fluid is re-pressurised within diverging section (5) the pressure increase raises its temperature to an elevated level which is higher than the temperature in the condenser. Advantageously this section is thermally isolated from the condenser to prevent any transmission of heat during this stage to the first working fluid. The ducted gas can then be expanded within a second turbine (7), or other suitable means of energy extraction. The condensed first working fluid exiting the condenser at (8) is now re-circulated in liquid form to a pump where it is re-pressurised, then passes to a heat source where it is vaporised, and then used to drive the first turbine (2) to generate electricity.

(8) When operating in energy storage mode, a gas is compressed by compressor (10) and transmitted into a hydrostatically pressurised unit or container (9), typically using off-peak or low demand electricity in compressor (10). In some embodiments compressor (10) could be the same, or part of the same component, as second turbine (7). It would also be possible to recover the thermal energy due to the heat of compression at this stage, possibly using that heat as an energy source to assist the compressor in order to increase overall efficiency levels. The hydrostatic pressure maintains the gas at a constant pressure throughout discharge allowing the condensing energy to be stored for later use within the Venturi condenser, avoiding an energy drain during generation to increase the maximum available output.

(9) In another alternative embodiment, the Venturi condenser may advantageously be provided with a plurality of Venturi tubes arranged to operate in parallel. The input to the tubes can be arranged to receive the second working fluid from the hydrostatic storage unit (9). An advantage of the plurality of Venturi tubes is that the heat exchanger means can be arranged to transfer heat more efficiently between first and second working fluids because of the closer proximity of the working fluids. Additionally, the gas flow in the Venturi tube can be maintained at or closer to the ideal linear flow, so maintaining the effectiveness and efficiency of the system.

(10) In another alternative embodiment, the Venturi condenser may comprise one or a plurality of Venturi tubes where at least one of these Venturi tubes include more than one converging and straight sections arranged in series to allow depressurisation to occur in stages, and where thermal energy is absorbed by the second working fluid in the intermediate stage or stages when the second working fluid is partially depressurised as well as when that fluid is fully depressurised in the final stage of depressurisation. An advantage of staged decompression over an equivalent single stage decompression is that the low temperature extremes which the first working fluid would be exposed to are reduced, which temperature extremes may have caused structural complications and ice formation.

(11) Referring to FIG. 2, there is shown a schematic diagram of a system in which a Venturi condenser powered by a hydrostatically pressurised gas which is used to extract energy from a hydrogen oxygen turbine generation and water electrolysis system. A water reservoir (11a) feeds a water feed (11) used by an electrolysis system (12) to produce hydrogen and oxygen gas which is gas stored under pressure in underwater storage means (13) and (14) and which water feed is supplied under hydrostatic pressure. The water feed shown is taken from exhaust steam from the turbine generator assembly (17) although it could also be externally sourced, possibly from surrounding water. The water reservoir (11a) is provided to accommodate the different fluid volumes of the electrolyser water feed. The electrolysis system (12) is supplied with an external source of electricity, typically off peak or low demand electricity, and used to produce hydrogen and oxygen gasses which are allowed to rise through pipe-work into storage units (13), and (14). Air is also compressed during a storage phase by a compressor (15) and transmitted through separate pipe-work into air storage unit (16). Each storage unit subjects its gas to a relatively constant hydrostatic pressure. A possible method of recovering the heat of compression and reusing that energy to increase efficiency is also shown. The method shown comprises a Rankine heat extraction cycle, which Rankine cycle vaporises the water supply using the available heat of compression and then transfers the steam to part of the expansion turbine (17) to generate electricity, which electricity is supplied to the electric motor to assist with driving the compressor. The steam is then condensed back to water and pumped back to the vaporiser. The storage units shown here in this example are flexible membranes contained within rigid ballasting outer structures. On demand, the hydrogen and oxygen gasses are released from storage means 13 and 14 under hydrostatic pressure and transmitted to the hydrogen oxygen turbine generator (17) where they are combusted in a combustion chamber (17a) in order to generate electricity. The air, from storage unit (16) is transmitted through at least one separate duct (16a) to a condenser (18). The condenser (18) provides condensing and heat recovery through the Venturi effect before being expanded through air motor or turbine (19). The air motor or turbine received output from the one or more Venturi tubes, the output from the Venturi tubes having sufficient energy to drive an air motor or turbine (19) which is coupled to a second generator (19a). Second generator (19a) provides an output to an external power supply. Alternatively, any power produced can be used to provide energy to operate the system.

(12) The oxygen gas in this embodiment is also transmitted through condenser (18). The oxygen is fed into the inlet portion of one or more Venturi tubes and as it passes through the Venturi tube it cools, expands and is re-pressurised on exit from the Venturi tube part of the condenser (18). Upon exiting the condenser the oxygen is fed to the combustion chamber (17a). An advantage of supplying oxygen gas at elevated temperature is that it raises the heat of combustion and increases the power output of the hydrogen oxygen gas turbine.

(13) The turbine generator set (17) includes a combustion chamber (17a) which receives oxygen from the Venturi condenser (18). Separate lines feed oxygen from an oxygen riser (40) to condenser (18) and then to combustion chamber (17a). A hydrogen riser (42) separately supplies hydrogen gas to the combustion chamber. A compressor unit (44) compresses steam, a portion of which has been recirculated following its expansion in turbines (46, 48), which recirculated steam is supplied to the combustion chamber.

(14) Output from the combustion chamber is used to drive one or more turbine sets (46, 48) to extract energy and generate electricity in generator (52). A low pressure turbine (50) receives some output from the turbine (46, 48) which is in gaseous form The remainder of the output not supplied to low pressure turbine (50) is recirculated, where it is passed through a heat exchanger means (54) in which the heat is extracted, and then compressed (44) and supplied to the combustion chamber. The extracted heat is transferred to the flow used to drive low pressure turbine (50). Output from the low pressure turbine (50) is passed to the Venturi condenser (18) which operates in a similar manner to that described above.

(15) This particular arrangement can be described as a form of combined cycle, where the combustion, expansion, and recirculation, and compression of a portion of steam form part of a closed Brayton cycle, and the extraction of heat from the Brayton cycle exhaust in a second portion of steam, the expansion of that second portion of steam in a turbine, and the condensing, pumping to pressure, and recirculation of that second portion of steam condensate form part of a bottoming Rankine cycle.

(16) Referring to FIG. 3, there is shown a system located within an adapted deep coal mine. Two vertical shafts have been converted. Shaft (20) contains a means of access to the electrolysis system (22) located at the bottom of the shaft below and also the power supply. Shaft (21) is flooded to provide hydrostatic pressurisation of the storage units, and contains pipe-work for the gasses and a separate column of water feed for the electrolysis system. This arrangement is by way of example only.

(17) Although the electrolyser shown is not submerged, its water feed is hydrostatically pressurised, which pressurisation can then directly be transferred to the gasses produced through electrolysis. The electrolysis system (22) may be housed within a part of a mine gallery (23) which is not flooded and is accessible through Shaft (20). Separator Section (24) separates the flooded section from the non-flooded section and contains the pipe-work for transmitting hydrogen and oxygen gasses and water supply. Section (25) is a flooded section subjected to hydrostatic pressure by the water column in (21), and contains the storage units which are shown as flexible membranes (26) containing gaseous hydrogen, oxygen, and air within different rooms in the mine. Any number of discrete units might be used for each of the gasses although only three are shown here. The gasses are variously supplied to a hydrogen and oxygen combusting gas turbine arrangement (27) operating in conjunction with a power generating system of the type shown in FIG. 1 and described above, a compressed air system (28), and a Venturi condenser (29). Variations in water level of the hydrostatic pressurisation fluid which may result from differing levels of gas storage can be accommodated by reservoir (30) which maintains the hydrostatic pressure at a relatively constant level.

(18) As described above, hydrogen and oxygen lines rise separately from the respective hydrostatically pressurised storage units (26). Operation of the system is similar to that described for FIG. 2 above.

(19) FIG. 4 shows an example of a parallel arrangement of Venturi tubes in a Venturi condenser. In this example there are only two tubes shown for simplicity and clarity but any suitable number could be deployed. Factors affecting the number of tubes include volume of fluid to pass through the tubes, the temperature difference between the fluid at the input region (4) and diverging output region (5). A further factor to be considered refers to the efficiency of the heat exchangers (not shown) surrounding the diverging portion of the Venturi tube.

(20) The inlet for the tubes is connected to a common conduit (4a) feeding working fluid to all the tubes. Each tube is provided with its own converging portion (4) diverging portion (5) and a central portion.

(21) Output from the tubes converges at (5a). The output from the Venturi condenser exits through a common output conduit to enter a secondary power turbine (7).

(22) FIG. 5a shows a different method of operation in which there is a multiple stage pressure reduction in pressure, which is referred to as a series type arrangement. An inlet portion (50) shows the inlet region in general. A first inlet portion (52) provides a first stage of pressure reduction. The incoming fluid will decrease in pressure and accelerate as it passes along the tube to a second converging region (54). In this region the pressure of the fluid is further reduced and accelerated before passing through a central region (56) in which it reaches its maximum velocity. The fluid then enters the diverging zone (58) where the velocity slows and pressure rises. Heat exchanger means (not shown) surround the diverging portion (58) and heat is transferred from a first working fluid to the second working fluid passing through the Venturi tube.

(23) FIG. 5b shows a graph of temperature and pressure variations along the tube.

(24) In the series arrangement, the intermediate stage could advantageously comprise multiple parallel tubes for the straight section to maintain laminar flow characteristics of the working fluid. An additional advantage is that it could enable a reduced wall thickness (and therefore facilitate heat transfer), and also increase contact area between the first and second fluids (again to facilitate heat transfer). In another embodiment, in order to preserve a symmetric shape, 2 flows could be used each flowing in opposite directions.

(25) It can be envisaged that in certain circumstances it would be advantageous to have both aspects of multiple stage and a parallel arrangement to Venturi tubes in a Venturi condenser.