WO2024047380A1

WO2024047380A1 - Micro electrical power generation from external combustion heat energy, using pressure swing on hot-oil liquid pistons (pslp)

Info

Publication number: WO2024047380A1
Application number: PCT/IB2022/058156
Authority: WO
Inventors: Ahmet KARAHAN
Original assignee: Karahan Ahmet
Priority date: 2022-08-31
Filing date: 2022-08-31
Publication date: 2024-03-07

Abstract

A micro power generation unit designed for domestic use, which converts externally generated heat energy to mechanical energy and subsequently to electricity, using hydraulic pressure, created by means of instantly produced steam. The mechanical energy conversion rate is relatively higher than the available micro power solutions and using the unit as a CHP, keeps overall efficiencies high. Regardless of the fuel type, the heat is generated externally in a combustion chamber, located under two pressure swing cylinders, which are half full with oil. The hot-oil reciprocates among the cylinders by means of steam pressure and performs mechanical work at the hydro-motor in between. The mechanical work is converted into electricity via an alternator. No steam boiler and no geartrain/crankshaft. The video of the conceptual test unit is under the link https://youtu.be/K0Arm9tif38.

Description

MICRO ELECTRICAL POWER GENERATION FROM EXTERNAL COMBUSTION HEAT ENERGY, USING PRESSURE SWING ON HOT-OIL LIQUID PISTONS (PSLP)

Background of the invention

This invention relates generally to a micro power generation unit, which converts a part of the externally generated heat, first to hydraulic pressure, then to mechanical power and finally to electricity for domestic use. In order to keep overall efficiencies high, it should be used as a CH P (combined heat and power) unit. In that case, the waste heat is recuperated back to a heating circuit.

Recent available technology

Nowadays, decentralized electricity production became one the major goals to increase overall efficiencies by decreasing transfer losses and to lower the investment costs for the infrastructure. Accordingly, there have been several attempts to design CHP systems with the aim to serve both heating and electricity needs of households.

However, due to the technical limitations in micro power degrees (1 -10kWs), most of them turned out to be unfeasible due to reasons like very poor efficiencies, very high investment costs, short service lifetime, high noise levels, big space requirements, safety regulations and precautions, etc.

The common commercialized CHP units use internal combustion engines (internally generated heat), which can only use liquid or gaseous refined fuels. High investment costs, short service lifetime, high maintenance costs and high noise levels can be stated as further disadvantages.

For externally generated heat (also appropriate for solid fuels incl. biomass), different types of heat engines like Stirling, Brayton, Ericsson engines and steam engines are tested in CHP systems. However, they could not commercially succeed due to low running speeds, big space requirements, low power to weight ratios and low efficiencies. The most promising one has been the application of the sliding multi-vane expander in an ORC (Organic Rankine Cycle). Nevertheless, lubrication and short service lifetime are still problems to overcome. Thermoelectric generators can also be mentioned, but are still too expensive, poor in efficiency and requires accurate temperature control for reliable operation. Aim of the invention

After all the dedicated research with many experimental setups to verify, the owner of this work concluded that, the solution for micro-power production from external heat was in hydraulic pressure. It was found as the best option to convert external heat energy into mechanical energy by relatively higher efficiency rates and affordable investment costs. To create the hydraulic pressure, steam is the outstanding and least costly option. However, to avoid a steam boiler and its safety requirements, steam pressure has to be produced instantly, whenever it is needed. This could only be achieved by an intermittent operation, in other words, by a swinging pressure operation.

Furthermore, leakages by using pressurized steam should be avoided for the sake of the efficiency. This encourages the use of the liquid piston concept. The temperature difference between steam and the piston has to be relevant and compatible, and accordingly hot-oil is chosen as the heating medium and as the pressurized liquid at the same time.

The system is named shortly after PSLP (Pressure Swing on Liquid Pistons), as there are liquid pistons considered, which are driven by a swinging pressure.

In addition to that, liquids with lower boiling temperatures like alcohol or ammonium or even several organic gases with low liquid pressures can be used for operations by low- temperature applications, if only required conditions for sealed loop (hermetic) operation are met and safety precautions are taken.

It does not require any gear train or crankshaft.

Explanation of the invention

The required heat energy is generated externally in a combustion chamber (10), which is incorporated underneath the pressure swing cylinders (1 ), (2) and equipped with a burner (for oil or gas fuels) or with a blower (for solid fuel or biomass) (3). The combustion system has its own control unit and runs according to the signal, sent from the main controller (52) in case of any heat demand. It also adjusts the air-fuel ratio for an efficient combustion.

While heating the pressure swing cylinders (1 ) / (2), it must be ensured by design that, not only the bottom, but the upper parts of cylinders are heated to roughly same temperatures. They must also possess a big enough heat-transfer surface area in accordance with the nominal power. On the way out, the combustion gases pass through another section, where a finned tube flue-gas heat exchanger (38) transfers the most of the remaining heat to the water in the heating circuit. The flue gas is then directed to the chimney.

Before starting with the power production, the pressure swing cylinders must be preheated to temperatures of around 220 °C. As the oil piping and its peripherals are still cold, a higher temperature than the acceptable minimum must be aimed. This way, excess temperature drop at the first run can be tolerated.

During the preheating, there is no pressure in the pressure swing cylinders at all. A vacuum even can exist at the very beginning as a consequence of the last run due to the condensation of the leftover steam and due to the shrinking of the cold oil. For that reason, the steam release motor-valves (23) and (24) are opened and kept open during the whole preheating mode, so that air in the cavities can freely move. The temperature of the oil is monitored with both temperature sensors (19) / (20). The amount of oil is supposed to be shared evenly under both pressure swing cylinders (1 ) and (2), since a timer in the software keeps recording the cycle durations and the stopping procedure is designed to be activated at the mid of the cycle at the prior run. After both temperature readings exceed 220 °C, the main controller (52) toggles to the operation mode.

At this point, before explaining the operation mode cycle, the design of the pressure swing cylinders I & II (1 ) (2) must be described:

In order to achieve a high overall efficiency rate, the cylinders with the combustion chamber, the whole oil installation and its peripherals must be insulated. The insulation must withstand high operating temperatures and must be sized for an average operating temperature of around 250 °C.

The steam outlet connection port must be located at the most upper part of the cylinder. The pressure in the cylinder is indicated by the manometer (25) I (26) and watchdogged by the pressure safety valve (27) I (28). Both have a common direct connection to the port. Following them, a steam release motor-valve (23) / (24) is installed to control the steam flow. Another connection port at the upper part is dedicated for the maximum oillevel switch (21 ) / (22).

There is an interior heat exchanger (15) I (16) incorporated into the cylinder for evaporation. The one end of the interior heat exchanger is connected to a port, which is located somewhere at the bottom part of the pressure swing cylinder. The interior heat exchanger is installed in such a way, that it is submerged in the oil and the other end opens to the cavity above the maximum oil-level. This way, the heat from the oil can easily be transferred to the metered water, which is to be pumped with pressure into the interior heat exchanger throughout the injector solenoid valve (11 ) / (12) and the injector check valve (13) I (14). The interior heat exchanger must have a sufficient heat-transfer surface area, to steam up the water and additionally to heat up the produced steam to the average temperature by passing through. The oil inlet /outlet port is located next to the very bottom part of the pressure swing cylinder, letting the oil flow over a service valve (29) I (30), just in case for any shut-off need. To get the cylinder drained for cleaning/service purposes, a plugged port at the very bottom part of the cylinder is also available.

For checking the permissible minimum oil-level, as well as the oil-temperature, the cylinder has been equipped with a minimum oil-level switch (17) / (18) and a temperature gauge (19) I (20).

Now, we can continue with the explanation of the operation mode cycle.

The operation mode cycle starts with pressurizing the pressure swing cylinder-l (1 ). First of all, the four-way motor-valve (4) is positioned, giving way the oil to flow from the pressure swing cylinder-l (1 ), (as stated with the marks ‘a’). The steam release motorvalve (23) of the pressure swing cylinder-l (1) is closed and the steam release motorvalve (24) of the pressure swing cylinder-ll (2) is opened. After a short delay for the position change of the motor-valves, the injector solenoid valve (11 ) of the pressure swing cylinder-l (1) injects the right amount of pressurized water (metered by the duty time) throughout the injector check valve (13) into the interior heat exchanger (15). As the interior heat exchanger (15) is submerged into the hot-oil bath, the entering water vaporizes instantly and the produced steam fills out the cavity at the top of the pressure swing cylinder-l (1) by being heated up additionally throughout the interior heat exchanger. The pressure in the pressure swing cylinder-l (1 ) increases.

The amount of the pressure in the cylinder depends on the average temperature of the upper cavity, on the heat-transfer surface area of the interior heat exchanger (15) and on the amount of water injected into it. To keep the average temperature high, the cylinder must be evenly heated inside and must be good insulated outside. The amount of the injected water is adjusted with the duty time of the solenoid valves (11 ) / (12), since the water pressure is kept quite stabile thanks to the pressure buffer tank (9) and the pressure switch (49). The hot-oil in the pressurized cylinder (1) is pushed over the four-way motor-valve (4) to the gear type hydro-motor (5), passing first the strainer (32) and then the high-pressure oil-filter (33). The hydro-motor (5) converts the high pressure of the hot-oil to mechanical power, which is then converted to electricity with the help of the clutched alternator (6). To clean up the strainer (32) and to change the high-pressure oil-filter (33), filter service valves (31) I (34) have been installed before and after.

The hot-oil returning from the hydro-motor (5) fills up the 'low' pressure cylinder (2) as directed by the four-way motor valve (4), until the maximum oil level switch (22) is triggered and sends signal to the main controller (52). The main controller (52) opens up the steam release motor-valve (23) of the 'high' pressure cylinder (1 ) to decrease the pressure and closes the steam release motor-valve (24) of the 'low' pressure cylinder (2) at the same time. It also changes the position of the four-way motor-valve (4) allowing the oil flow the other way around (as stated with the marks ‘b’). From that point of the cycle on, the pressure swing cylinder-ll (2) becomes the 'high' pressure cylinder and the pressure swing cylinder-l (1 ) becomes the 'low' pressure cylinder. And the oil flow cycle repeats the other way around.

The steam expelled from the pressure swing cylinders (1 ) and (2) is directed over the steam check valve (35) to the condensing tank (7). The steam has been released down below the diffuser (36) located at the bottom of the tank, which is already half-filled with treated demineralized water. The available water with a temperature below 90 °C takes the heat of the steam and lets it condensate in itself. The condensation heat is further transferred to the heating circuit via the condensing tank heat exchanger (37). To avoid any further heat-loss, the condensing tank (7) is insulated as well.

Due to the high operating temperatures, it is inevitable that a small amount of oil will also evaporate and get transferred to the condensing tank (7). There, after being condensed, it will float over the available water layer and will keep accumulating. To control the levels of the oil and water separately, the condensing tank (7) has been equipped with a maximum liquid-level switch (41 ) and two additional submerged liquidlevel transducers (39) and (40). Either any signal from the minimum oil-level switches (17) / (18) or the combination of the liquid-level transducers' signals (39) / (40) and the maximum liquid-level switch (41), would be the signal for a break in operation for maintenance, in order to feed the deposited oil back into the cylinders. Feeding back the expelled oil can also be done via full automation.

The condensing tank (7) is open to the atmospheric pressure via an air-vent (42). It has an oil dispensing outlet valve (43), and a service drain valve (44). The accumulated condensed water is delivered through the condensate outlet valve (45) and the condensate strainer (46) to the water pump (8), which pressurizes the demineralized water in the line supplying the injector solenoid valves (11 ) / (12). The pressure is stabilized with the help of a pressure-water check valve (47) and a pressure buffer tank (9) at around 6-7 bar-g. It is being watchdogged with the pressure switch (49). In case of any service need, the water in the pressure buffer tank (9) can be drained back to the condensing tank using the pressure-water drain valve (48) and the air-pressure in it can be balanced with the air service valve (51 ). The injection pressure can be observed from the water pressure manometer (50) on the pressure buffer tank (9).

If we reconsider some of the details regarding the components and the operation of the system, the following remarks can be pointed out:

The pressure swing cylinders (1) I (2) must withstand high flame-temperatures and the corrosive environment.

The oil, which is also used as the liquid piston, must be a synthetic type with a kinematic viscosity @ 40°C (DIN EN ISO 3104) of around 150 mm²/s and with a viscosity index of around 200. It must have an autoignition temperature (ASTM E659) higher than 400 °C. Taking necessary precautions by design, even hydrocarbons with long chains like paraffin can be used, which is in solid state phase at room temperatures, but will be in liquid state at operating temperatures.

Not only the hydromechanical parts like the hydro-motor, the four-way motor-valve or the solenoid valves etc., but also all the oil piping and installation parts including the sensors and switches must be appropriately modified to operate at temperatures of around 250 °C and at a pressure of 40 bar-g. They also must be made of materials resistant to hot-oil.

The water in the injection system must be demineralized. Its piping and the pressure buffer tank (9) must be corrosion resistant as well.

The diffuser (36) at the bottom of the condensing tank (7) can just be a piece of perforated plate or a wire mesh, which are corrosion-resistant.

As the alternator (6), an AC or a DC type can be used. By the AC type alternator, the produced electricity must be converted with an AC/DC rectifier (53) to direct current first. The electricity, produced and buffered in a small battery-pack (54), can then supply an off-line electrical circuit or back-feed the mains net via an appropriate inverter (55).

The hydro-motor (5) must be a gear-type one, since a higher running speed rather than a higher torque is desired. The displacement of the hydro-motor can be calculated with commonly used formulas by taking the desired input heat power, the desired running speed and being on the safe side, by taking the average hydraulic pressure as 15 bar-g and the assumed conversion efficiency rate as 5%.

For aligning the direction of the pressurized oil to the hydro-motor, we can also use a setup of four separate swing check valves, instead of using the four-way motor valve (4). Actually, it is a basic and cheap solution. However, to keep the hydraulic loop simple to be understood, the scheme with the four-way motor valve is chosen.

Regarding the efficiency and the output power, we can say that, metering the right amount of the injected water plays a very important role on the efficiency rate and on the power output.

Considering the amount of the injected water; if the amount of the equivalent saturated steam volume slightly exceeds the total volume of the moving oil, we may talk about the saturated steam pressure for that average temperature of the cavity. If the amount of the equivalent saturated steam volume is less than the total volume of the moving oil, we may talk about superheated expanding steam. In the latter case, the thermal efficiency must be higher, but the power output will be less.

Respectively, injecting excess amounts of water will drastically decrease the efficiency due to the unused steam and also the operation speed, as the steam releasing time would linger.

Another factor, effecting the efficiency, is the total amount of the volume, existing in the upper cavity of the filled pressure swing cylinder and in the inside of the interior heat exchanger. The less the volume is, the higher is the efficiency.

The probable application in industries

In particular at places, where there is no mains net, it can be used as a CH P unit, which does not require any refined energy source and can cover micro-power needs and heatdemands with relatively less amounts of investment and with relatively higher conversion rates.

In addition to that, waste heat recovery at micro-power degrees can be achieved with comparably less investment by hermetic operations, which use organic liquids with low evaporation temperatures.

The copies of this work have been notarized as the affidavit of Ahmet Karahan (Mechanical Engineer B.Sc.) by the Notary Public 4th of Kadikoy Istanbul / Turkish Republic on the 24th of August 2022.

The video, showing the operation of the inventions conceptual test unit can be found under the YouTube channel of the owner, following the link https://youtu.be/K0Arm9tif38 Description of the drawings

FIG.- 1 The schematic diagram of the present invention, which comprises four main sections: Power generation (framed and labeled), pressurized water preparation (framed and labeled), condensation (framed and labeled) and all the rest about the heat and hydraulic pressure generation.

FIG.- 2 The schematic diagram of the oil-flow for a full cycle.

FIG.- 3 Only the control elements, including the main controller and the electromechanical components, as well as the sensors and switches.

References in figures

1 ) Pressure swing cylinder -I

2) Pressure swing cylinder -II

3) Burner I Blower

4) Four-way motor-valve

5) Hydro-motor

6) Alternator

7) Condensing tank

8) Water pump

9) Pressure buffer tank

10)Combustion chamber

11 ) Injector solenoid valve -I

12)lnjector solenoid valve -II

13) Injector check valve -I

14) Injector check valve -II

15) Interior heat exchanger -I

16) Interior heat exchanger -II

17)Minimum oil-level switch -I

18)Minimum oil-level switch -II

19)Temperature gauge -I

20)Temperature gauge -II

21 )Maximum oil-level switch -I

22)Maximum oil-level switch -II

23)Steam release motor-valve -I

24)Steam release motor-valve -II

25)Manometer -I 26)Manometer -II

27) Pressure safety valve -I

28) Pressure safety valve -II

29)Service valve -I

30)Service valve -II

31 )Filter service valve - before

32)Strainer

33)High pressure oil-filter

34) Filter service valve - after

35)Steam check valve

36) Diffuser

37)Condensing tank heat exchanger

38)Flue-gas heat exchanger

39) Liquid-level transducer - Min.

40) Liquid-level transducer - Max.

41 )Maximum liquid-level switch

42)Air-vent

43)Oi I dispensing outlet valve

44)Service drain valve

45)Condensate outlet valve

46)Condensate strainer

47) Pressure-water check valve

48) Pressure-water drain valve

49) Pressure switch

50)Water pressure manometer

51 ) Air service valve

52)Main controller

53)AC/DC rectifier

54) Battery-pack

55) Inverter

Claims

CLAIMS ) This invention is a micro electrical power generation unit, which converts external combustion heat energy to electricity and comprises;

- An external combustion chamber (10), wherein the combustion is carried out under controlled air-fuel ratio,

- Two pressure swing cylinders (1 ) / (2) of the same volume and shape, which serve as the heat transfer element and as well as the liquid piston cylinders and contain the amount of oil, just enough to fill up only one of them,

- A water pressurizing unit with a stable pressure, which supplies the right amount of pressurized water at the right time of the cycle, to inject into the interior heat exchanger (15) I (16), embedded in the pressure swing cylinder (1 ) / (2),

- A hot-oil hydraulic circuit with a four-way motor-valve (or with a setup of 4 separate swing check valves), which arranges the hot-oil flow accurately into the right direction of the filter- and hydro motor- inlets, created by the liquid piston push as a result of evaporation of the water, which is pumped into the other cylinder in row on each half-cycle.

- A hydro motor (5) modified for operating temperatures as high as 250 °C and its filter set (32) (33), which converts the created hydraulic energy to mechanical energy,

- Shut-off motor (or solenoid)-valves (23) / (24) to release the steam in the pressure swing cylinders after having performed work.

- A condensing tank (7) for cooling and collecting, in order to condense the steam, which has already performed its work in the pressure swing cylinders in order to reuse the water, - An electricity generating gearset, consisting of a DC or AC alternator (6) to convert the created mechanical energy into electricity; of an AC/DC rectifier (53) and of a small battery-pack (54) to buffer the blackouts during pressure swings and of an inverter (55), either for an AC power supply from that battery-pack or to back-feed the mains net.

- A main controller unit (52) with the adequate software, to let all the cycle steps electromechanically run with proper timing and sequence and to ensure a safe and reliable operation based on the interpretation of the gathered data from the sensors.

- A connection to a domestic heating circle, which recuperates not only the condensation heat gained in the condensing container, but the excess heat from the flue gases as well.

2) The micro electrical power generation unit according to Claim 1 ., wherein said an external combustion chamber (10) with controlled air-fuel ratio has the ability to adapt the heat power amount based on the signal coming from the main controller unit (52).

3) The micro electrical power generation unit according to Claim 1 ., wherein two pressure swing cylinders (1 ) / (2) of the same volume and shape, which serve as the heat transfer element and as well as the liquid piston cylinders and contain the amount of oil, just enough to fill up only one of them, are placed on the combustion chamber (10) side by side.

4) The two pressure swing cylinders, which are placed on the heating chamber side by side according to Claim 3. have big enough heat transfer surface areas to enable the highest amount of heat-transfer from the flue gases to the oil inside the cylinders and to the produced steam as per the nominal design power.

5) The two pressure swing cylinders, which are placed on the heating chamber side by side according to Claim 3. have an interior heat exchanger (15) (16) each, with a big enough heat transfer surface to evaporate the amount of water, which is pumped metered into it at each cycle, and further to heat up the produced steam to the operating temperature while passing through, so that direct contact of the water with the hot-oil is avoided. The interior heat exchanger, which is submerged in hot-oil inside the cylinder, has one end connected to a port opening to the outside and the other end open to the cavity over the oil level at the top of the cylinder.

6) The two pressure swing cylinders, which are placed on the heating chamber side by side according to Claim 3. must be equipped with oil level sensors (17) (18) (21 ) (22) capable of functioning at those high operating temperatures to signal the maximum and minimum hot-oil levels to the main controller unit (52).

7) The two pressure swing cylinders, which are placed on the heating chamber side by side in according to Claim 3. must be equipped with temperature sensors (19) (20) to inform the main controller unit (52) about the temperature of the hot-oil inside the cylinders, as the unit can only operate in a temperature range.

8) The two pressure swing cylinders, which are placed on the heating chamber side by side according to Claim 3. must withstand an operating pressure of 45 bar-g and must be heat-insulated for the operating temperature of 250 °C.

9) The micro electrical power generation unit according to Claim 1 ., wherein said a water pressurizing unit with a stable pressure, which supplies each pressure swing cylinder with the right amount of pressurized water at the right time of the cycle is connected to each of the interior heat exchangers (15) / (16) inside the cylinders over a fast-reacting solenoid valve (1 1 ) / (12) and a check valve (13) / (14) in line to hinder the water from coming back out.

10)The micro electrical power generation unit according to Claim 1 ., wherein said a condensing tank (7) for cooling and collecting, in order to condense the steam and reuse the water, which has already performed work in the pressure swing cylinders, must include a diffuser (36) to spread the coming steam into the available water. )The condensing tank for cooling and collecting, which has a diffuser to spread the coming steam into the available water according to Claim 10., is equipped with liquid level sensors (39) (40) (41) in order to detect and control the oil and water levels separately. )The condensing tank for cooling and collecting, which has a diffuser to spread the coming steam into the available water according to Claim 10., has a condensing tank heat exchanger (37) inside to transfer the condensing heat to the heating circuit. )The micro electrical power generation unit according to Claim 1 ., wherein said a connection to a domestic heating circuit, which recuperates not only the condensation heat gained in the condensing container, but the waste heat from the flue gases as well, has been achieved by letting the returning water from the heating circuit first enter the condensing tanks heat exchanger (37) and then the flue gas heat exchanger (38), which is installed into the flue way after the cylinders. The water of the heating circuit goes back to the heating zone then.