Generator for a natural gas pressure reduction station

Abstract

An electrical generator system and method for a pressure reduction station PRS. A gas pump which is connected to a gas supply of the PRS and which generates mechanical energy from the flow of gas through the gas pump, an air pump which is mechanically coupled to the gas pump and which generates compressed air from its movement and an output conduit which connects the compressed air to an electrical generator wherein the electrical generator generates electricity from the compressed air.

Description

[0001] Generator for a Natural Gas Pressure Reduction Station

[0002] Field of Invention

[0003] The present invention relates to a generator, suitable for use in a natural gas Pressure Reduction Station (PRS) and in particular to a generator which harvests energy from the PRS.

[0004] Background of the Invention

[0005] Natural gas (also called fossil gas, methane gas or simply gas) is a fuel which comprises a mixture of gaseous hydrocarbons consisting primarily of methane and various smaller amounts of other higher alkanes. Low levels of trace gases like carbon dioxide, nitrogen, hydrogen sulphide, and helium are also usually present. Natural gas is odourless therefore, odourisers such as mercaptan are commonly added to it for safety so that leaks can be readily detected.

[0006] Natural gas is used as a fuel either at a power station to create electricity or is burned directly in a gas boiler in a commercial, industrial, or domestic setting. Typically piped natural gas is transported at elevated pressure to the outskirts of large demand, areas of population or commercial or industrial estates.

[0007] Gas pressure reduction stations (PRS), also known as pressure regulator stations, are crucial components of the natural gas distribution infrastructure. They play a vital role in ensuring the safe and efficient delivery of natural gas to end-users.

[0008] A PRS is designed to control and lower natural gas pressure as it moves through the distribution network. Its primary purpose is to reduce the high-pressure gas received from transmission pipelines to a level suitable for local distribution systems and endusers.

[0009] Natural gas is 84 times more harmful than carbon dioxide and a reduction in the average gas network system gas pressure has a huge impact on gas leakage and subsequent environmental impact. COP28 set targets and countries agreed to reduce natural gas emissions by 50% over the next 6 years, this will be challenging. Figure 1 is a schematic diagram of a known pressure reduction system (PRS) 1 . It shows a housing 3, the interior 5 of which comprises a high pressure gas input 7 connected to an input high pressure valve 9, a filter 11 for purifying the input gas, a regulator 13 which reduces the gas pressure, a monitor regulator or slam shut 14 and an output low pressure valve 15 coupled to the output 17.

[0010] A typical PRS has one or more gas streams, each stream comprises of an inlet control valve and a regulator which regulates the incoming high-pressure gas to maintain the desired reduced outlet pressure and an outlet control valve. The two control valves enable the flow of gas to be temporarily stopped so that the regulator is isolated, to enable planned maintenance to be undertaken. The pressure regulation process begins with the gas passing through an in-line filter to remove impurities. It then enters the pressure regulator, which adjusts the flow rate and reduces the pressure to the desired level. The pressure regulator modulates pressure based on demand to provide a constant downstream pressure monitored by telemetry at one or more low points or monitored at source.

[0011] Gas pressure reduction is primarily achieved by gas restriction typically by means of a spring-loaded valve pressure regulator or a pilot-operated pressure regulator valve. PRSs incorporate safety features, such as relief valves, slam shuts and pressure regulator, to protect against over pressure and under pressure conditions. These mechanisms are crucial in preventing over pressurisation incidents and maintaining the integrity of the gas distribution system.

[0012] Typically, a PRS governor / regulator reduces the incoming gas pressure to “LP” or Low Pressure, the value range of this is typically 23.0 mb to 75.0 mb. The actual supply pressure can change with gas demand if it is too low, it will be insufficient to provide end users with a viable and safe supply. In the UK, the minimum mandatory value is 18.5 mb at the inlet to the consumers gas meter. Intermittent low pressure can represent a danger to consumers as pilot lights may be extinguished and appliances may fail to operate. Too high a pressure increases leakage which increases costs, gas shrinkage volumes and an adverse environmental impact A small decrease in average system pressure has a dramatic and positive impact on gas shrinkage / leakage. Therefore, on many gas networks pressures are monitored manually and with telemetry to remotely adjusted the pressure to achieve optimum minimum values.

[0013] One challenge is how to obtain sufficient uninterrupted electrical power to operate pressure control systems, telemetry, and other safety monitoring systems.

[0014] The current practice is to utilise rechargeable and non-chargeable lead acid deep cycle gel batteries. These are located securely outside of the PRS which is rated as an ATEX or LIKEX safe zone area.

[0015] Battery charging or exchange is time consuming and costly, requiring at least one visit to site and there are very many sites. Where a power supply issue has arisen, the system will default to a higher safety gas pressure being delivered to the network. This is until a visit to the PRS can re-establish the power supply. If the battery fails before it can be changed most systems will fail to a safe higher pressure setting until the sites battery has been changed and returned to its normal operating mode.

[0016] Various potential solutions have been tested to better provide the necessary power. Solar panels and micro wind turbines have been used. However, many PRS have in-built explosion relief roofs, this is a safety feature that in the event of a major fault condition and subsequent ignition of a flammable atmosphere, the explosive force will be directed upwards and away from passers-by, the installation of solar panels or a wind turbine could compromise this function. They would increase the design cost and installation and are liable to theft and vandalism.

[0017] In addition, the physical location, and the small size of some PRS roof area, physically limit the size of solar panel arrays making renewable energy non-viable in many locations.

[0018] Some PRS are also surrounded or shielded by buildings or trees which prevent sufficient power generation and debris must be removed on a regular basis and solar panels cleaned. Also, an expert assessment is required to ensure renewable energy options can be installed in a safe zone and will not compromise the explosive roof mechanism, these assessments are costly, site specific and time consuming. .

[0019] Summary of the Invention

[0020] It is an object of the present invention to reduce natural gas emissions within gas distribution networks.

[0021] In accordance with a first aspect of the invention there is provided an electrical generator system for a pressure reduction station PRS, the system comprising: a gas pump which is connected to a gas supply of the PRS and which generates mechanical energy from the flow of gas through the gas pump; an air pump which is mechanically coupled to the gas pump and which generates compressed air from its movement; and an output conduit which connects the compressed air to an electrical generator wherein the electrical generator generates electricity from the compressed air.

[0022] Preferably, the gas pump is a linear pump.

[0023] Preferably the air pump is a linear pump.

[0024] Preferably, the gas pump comprises a double acting cylinder and the compressor comprises a double acting cylinder wherein the gas pump and the air pump are configured as a master cylinder and a slave cylinder respectively, wherein the master cylinder is powered by differential natural gas pressures which causes the slave cylinder to move in the same linear motion thereby causing air at atmospheric pressure to be compressed at each piston stroke.

[0025] Preferably, the air pump is attached to a stepper motor enabling electrical power to be generated outside of the PRS in a safe zone.

[0026] Preferably, the gas pump is located inside the PRS.

[0027] Preferably, the air pump is located inside the PRS. Preferably, the electrical generator is located outside the PRS. In safe zone and so is not subjected to compliance with ATEX or LIKEX ratings or assessments.

[0028] Preferably, the gas pump is fed with high pressure input gas from a PRS input.

[0029] Preferably, the gas pump is located between a gas input valve and a regulator in the PRS.

[0030] Preferably, the electrical generator provides power to a control system which controls the operation of the PRS.

[0031] Preferably, the electrical generator provides power to a monitoring system which monitors the operation of the PRS.

[0032] Preferably, the electrical generator provides power to a telemetry system which provides a communications link to the PRS.

[0033] Preferably, the generator comprises a multi-piston high torque radial generator attached to a stepper motor.

[0034] Preferably, the generated electricity is alternating current (AC).

[0035] Preferably, the system further comprises a rectifier for converting AC to direct current (DC).

[0036] Preferably, the system further comprises a battery for storing the generated DC.

[0037] Preferably, the system further comprises an air return conduit for returning air that is exhausted by the radial generator back to the input of the air compressor for reuse so that filtration of new air is minimised, so extending the period for planned maintenance for air filter cleaning.

[0038] Preferably the electrical generator is housed in a cabinet which is outside the PRS. Preferably, the cabinet has an external non return valve and air intake together.

[0039] Preferably, the cabinet has an air filter.

[0040] In at least one embodiment, the gas pump does mechanical work by compressing gas, often air.

[0041] In accordance with a second aspect of the invention there is provided a method for generating electricity for a pressure reduction station PRS, the method comprising: Connecting a gas pump to a gas supply of the PRS and which generates mechanical energy from the flow of gas through the pump ;

[0042] Using the mechanical energy to generate compressed air within a cylinder Providing the compressed air to an electrical generator wherein the electrical generator generates electricity from the compressed air.

[0043] Preferably, the gas pump is located inside the PRS within a hazardous zone “zone 0”.

[0044] Preferably, the air compressor is located inside the PRS within a hazardous zone “zone 0”.

[0045] Preferably, the electrical generator is located outside the PRS “safe zone”.

[0046] Preferably, the gas pump is fed with high pressure input gas from a PRS input.

[0047] Preferably, the gas pump is located between a gas input valve and a regulator in the PRS.

[0048] Preferably, the electrical generator provides power to a control system which controls the operation of the PRS.

[0049] Preferably, the electrical generator provides power to a monitoring system which monitors the operation of the PRS. Preferably, the electrical generator provides power to a telemetry system which provides a communications link to the PRS.

[0050] Preferably, the generator is an air powered pump attached to a stepper motor.

[0051] Preferably, the generated electricity is AC.

[0052] Preferably, the system further comprises a rectifier for converting AC to DC.

[0053] Preferably, the system further comprises a battery for storing generated DC.

[0054] Preferably, the system further comprises an air return conduit for returning air to the housing after use for reuse.

[0055] Preferably the electrical generator is housed in a cabinet which is outside the PRS.

[0056] Preferably, the cabinet has an external non return valve and air intake together.

[0057] Preferably, the cabinet has an air filter.

[0058] Preferably, the gas pump which is connected to the gas supply of the PRS via a conduit which diverts a portion of the gas to the gas pump which has sufficient volume to operate the gas pump.

[0059] Preferably, the portion is less than 10% of the gas.

[0060] Preferably, the portion is less than 1 % of the gas.

[0061] Brief Description of the Drawings

[0062] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which:

[0063] Figure 1 is a schematic diagram of a known pressure reduction system (PRS); Figure 2 is a schematic diagram of an example of a generator in accordance with the present invention used in a PRS ;

[0064] Figure 3 is a schematic diagram of an example of a generator in accordance with the present invention;

[0065] Figures 4a and 4b is a schematic diagram which shows the extension stroke and return stroke of a double acting cylinder as used in at least one example of the present invention; and

[0066] Figures 5a is a schematic diagram which shows a control valve for use in at least one example of the present invention, figure 5b is a schematic diagram which shows an example of gas and air pumps used in a PRS in accordance with the present invention and figure 5c is a schematic diagram which shows an example of an electrical generator in accordance with the present invention.

[0067] Detailed Description of the Drawings

[0068] In at least one embodiment, the present invention utilises the differential gas pressures from inlet to outlet to power a pump that creates compressed air. In at least one embodiment, the solution provided by the present invention is fully mechanical with no physical connection between the gas and air nor any electrical components in the PRS and is, therefore, exempt from stringent zone rating.

[0069] Figure 2 is a schematic diagram of an example of a generator in accordance with the present invention used in a PRS. It shows a pressure reduction station 21 which comprises a housing with an interior space 25. The gas supply housed in the interior space 25 comprises a high-pressure input conduit which has a high pressure valve 29 and filter 31 . Pipe 34 has a diameter significantly smaller than pipe 32 and supplies a small volume of gas, typically less than 1 % of main pipe volume) from main pipe 32 to the gas actuated motor 39. The gas actuated motor 39 uses the gas pressure in the pipe 34 to drive a pump which powers the air compressor 41 . Once the gas has been used to drive the gas actuated pump it goes through the output low pressure valve and downstream into the LP network. In this example, the generated compressed air passes through an output conduit 43 and feeds an electrical generator 45 where the compressed air creates electricity. The electricity may be used directly in the control / monitoring equipment 47 or may be converted to DC for storage in a battery. A wired link 49 is the means for sending and receiving control / monitoring signals to and from equipment in the housing and arrow 51 denotes a communications link.

[0070] Comms link 51

[0071] Figure 3 is a schematic diagram of an example of a generator system in accordance with the present invention. The generator system 61 comprises a gas pump 39 and air compressor 41 connected to an electrical generator 45. The gas driven pump receives high pressure gas 67 uses it to power and air cylinder 41 . The compressor 41 has an input 63 which collects ambient air and an output 65 which sends compressed air to the generator 45.

[0072] Figures 4a and 4b show the extension stroke and return stroke of a double acting cylinder as used in at least one example of the present invention. Cylinder 81 has a piston 83 with a rod 85, piston seal 91. Pump flow 87 and return flow 89 are shown for the extension stroke 93. Pump flow 97 and return flow 99 are also shown for the return stroke 95

[0073] A gas linear pump (powered by gas creating compressed air) is connected to a gas supply of the PRS which generates mechanical energy from the flow of gas through the gas pump.

[0074] The gas pump comprises a master double acting cylinders powered by differential natural gas pressure and the air pump comprises a slave double acting cylinder. The linear motion of the master gas cylinder causes the attached air cylinder to also move in the same linear motion. Causing air at atmospheric pressure to be compressed at each piston stroke. The action of compressing air is achieved by cycling a master double acting cylinder which is mechanically attached to a slave cylinder of exactly the same stroke length. The air cylinder has two attachments on both ports, these consist of a tee or y branch containing two non-return valves. These are orientated such that one feeds forward the other feeds in reverse.

[0075] Non-return valves combine both air outputs which are connected to an air pressure line that feeds compressed air outside of the PRS to a multi-piston air motor which has relatively high torque this is permanently attached to a stepper motor enabling electrical power to be generated outside of the PRS is a safe zone.

[0076] As the piston travels within the cylinder, it causes air to be drawn through one of the non-return valves and into the cylinder chamber. When the piston reverses direction the drawn in air is compressed and expelled through the other non-return valve. This process is repeated at both ends of the cylinder such that the flow of compressed air is continuous.

[0077] In the following example, Figures 5a is a schematic diagram which shows a control valve for use in at least one example of the present invention. It comprises a 7 port control valve with ports labelled A-G as shown.

[0078] Figure 5b is a schematic diagram which shows an example 111 of gas and air pumps used in a PRS in accordance with the present invention. It shows a gas pump 113 coupled to an air pump 115. In particular, a gas input 117 is connected to a double acting gas cylinder 119, linear motion reversing switch 121 and linear motion reversing switch 123, conduit 125, double acting air cylinder 127 and gas output 129, 130.

[0079] For example, in the UK, distributed pressurised natural gas, typically with pressures of ranges between 0.35 to 7.0 Barg, upstream, enters the 7 port gas control valve 101 at the central port (A). It then exits at port (B) and enters a gas cylinder 119 at port (H). The present invention is usable in countries where different gas distribution regimes are in use. This gas pressure causes the piston contained within the gas cylinder 119 to extend linearly until it reaches a stop (Y) a mechanical pneumatic valve 123 is activated; this reverses the direction of gas flow within the 7-port gas control valve.

[0080] The gas flow direction is redirected such that gas again entering port (A) then exits port (C) and enters port (I) causing the piston to reverse its direction and to move linearly until stop (X) is activated by a mechanical pneumatic valve 121 .

[0081] This sequence is repeated multiple times.

[0082] Gas exits the gas control valve either at port (D) or port (E) where the pressure is switched, before being directed back into the outflow downstream gas stream without loss or venting.

[0083] The motion of the gas master cylinder causes the air slave cylinder 127 to undertake the same linear motion. This cylinder becomes the air compression device.

[0084] The air cylinder has a tee piece on both cylinder pipe air connections (ports) together with two non-return valves located on each tee.

[0085] Figure 5c is a schematic diagram which shows an example of an electrical generator 131 in accordance with the present invention. It shows air in 133, air out 135, a multicylinder air motor 137, a stepper motor 139 and power generation 141 .

[0086] When the cylinder cycles it causes the input of air into the cylinder entering at near atmospheric pressure and when expelled the non-return valve directs the compressed air flow to be expelled.

[0087] The compressed air via pipework is directed via pipework to an external safe zone where it acts upon a multi-cylinder rotary air motor contained in a protective enclosure.

[0088] The air motor 137 is directly connected via a drive shaft to a stepper motor 139 which upon rotation, generates ac power 141 , typically 15 volts to enable voltage rectification such that different chemistries of battery can be recharged. The rotary air motors exhausted air then returns via pipework back to the air cylinder where it is again directed and compressed to repeat with two modes, either continuous power generation or upon demand.

[0089] A non-return valve and air filter ensures slight positive pressure within the pipe work loop such that no air borne debris can ingress and to cause premature wear and so reduce mean time to failure and reliability of the power harvesting system.

[0090] In at least one example of a system in accordance with the present invention, the AC voltage output of the stepper motor is rectified to DC voltage, this can be used to charge a battery and / or can be utilised continually to power telemetry and control systems depending upon requirements together with a small back up battery in the event of a failure and so avoiding a default high pressure output should the generator system fail.

[0091] In at least one embodiment, the gas motor is of a type referred to as a pneumatic motor (air motor), or compressed air engine. In general, these devices do mechanical work by expanding compressed gas, often air. Pneumatic motors generally convert the compressed air energy to mechanical work through either linear or rotary motion.

[0092] In one embodiment, the gas motor comprises a vane motor a simple example of which has a circular rotor rotating inside a larger circular cavity. The centres of these two circles are offset, causing eccentricity. Vanes are mounted in slots cut into the rotor which contact with the housing to define chambers. In use, the gas enters an inlet chamber. The gas pressure at the inlet acts on the pistons and turns the rotor. Advantageously, a double acting cylinder compressing air consumes a significantly lower volume of gas and so when customer gas demand is low, for example, at night and in the summer, the small volume of gas input onto the network will not compromise the desired minimum outlet pressures. An important feature for long resilient operation is that the compressed air is substantially recycled in a loop, thereby limiting the potential to block incoming air filters with air borne debris. There are both supply and return air pipes to and from the gas / air pump, an external non return valve and air intake together with a large cleanable filter is contained within the external cabinet. As the air is substantially in a closed loop when in operation only small volumes of incoming air will require to be filtered.

[0093] The advantages of such a system is that it is may be easily retrofitted to existing PRS’s and may be provided in kit form for ease of installation regardless of the size or location. Once installed, the system of the present invention provides a reliable and sufficient power to meet the power requirements of all PRS.

[0094] In one example, the kit may comprise one external heavy-duty wall mounted enclosed cabinet with typical dimensions of 150x300x400mm. The rugged construction and attachment in a safe zone makes the cabinet less likely to be damaged or removed when subjected to vandalism or attempted theft.

[0095] Another advantage of the present invention is that because the design is mechanical in nature, the expert ATEX / Design appraisal will be simplified. Simplification of this process will save both time and money.

[0096] In at least one embodiment, the small volume of gas exiting the pump may pass through an approved gas network approved combined pressure regulator / slam shut, and it is then injected downstream into the LP network with no venting to atmosphere and no adverse environmental impact.

[0097] Other technologies such as a gas-powered turbine have been attempted but these are not rated at zone 0 and require a much larger flow of gas to operate and when compared to double acting cylinders have a shorter mean time to failure.

[0098] When this volume of gas is vented back into the gas network when there is very low gas demand such as during the summer months, in the early morning the downstream venting gas could potentially elevate the downstream network pressures and so compromise the intention to keep pressures to a minimum.

[0099] Advantageously, the present invention provides a “one size fits all” two devices one within the kiosk a pump and a small cabinet containing a generator on the outside, this will accommodate a wide range of gas inlet and outlet pressures and solve the challenge of providing power to any size or configuration of PRS. Energy harvesting system for pressure reduction stations where the differential pressure is utilised to compress air to generate electrical power in a safe zone.

[0100] The present invention provides an energy harvesting solution where the gas is vented downstream back into the network such that it has no impact on downstream pressures. The energy harvesting system may be provided in kit form so that installation time and complexity is kept to a minimum with no requirement for expert installation analysis that might compromise mandatory requirements. The foregoing description details presently preferred embodiments of the present invention. Numerous modifications and variations in practice thereof are expected to occur to those skilled in the art upon consideration of these descriptions. Those modifications and variations are intended to be encompassed within the claims appended hereto.

Claims

Claims1 . An electrical generator system for a pressure reduction station PRS, the system comprising: a gas pump which is connected to a gas supply of the PRS and which generates mechanical energy from the flow of gas through the gas pump; an air pump which is mechanically coupled to the gas pump and which generates compressed air from its movement; and an output conduit which connects the compressed air to an electrical generator wherein the electrical generator generates electricity from the compressed air.

2. An electrical generator system as claimed in claim 1 wherein, the gas pump is a linear pump.

3. An electrical generator system as claimed in claim 1 or claim 2 wherein, the gas pump is a linear pump.

4. An electrical generator system as claimed in any preceding claim wherein, the air pump is a linear pump.

5. An electrical generator system as claimed in any preceding claim wherein, the gas pump comprises a double acting cylinder and the air pump comprises a double acting cylinder wherein the gas pump and the air pump are configured as a master cylinder and a slave cylinder respectively, wherein the master cylinder is powered by differential natural gas pressures which causes the slave cylinder to move in the same linear motion thereby causing air at atmospheric pressure to be compressed at each piston stroke.

6. An electrical generator system as claimed in any preceding claim wherein, the air pump is attached to a stepper motor enabling electrical power to be generated outside of the PRS in a safe zone7. An electrical generator system as claimed in any preceding claim wherein, the gas pump is located inside the PRS.

8. An electrical generator system as claimed in any preceding claim wherein, the electrical generator is located outside the PRS.

9. An electrical generator system as claimed in any preceding claim wherein, the gas pump is fed with high pressure input gas from a PRS input.

10. An electrical generator system as claimed in any preceding claim wherein, the gas pump is located between a gas input valve and a regulator in the PRS.

11. An electrical generator system as claimed in any preceding claim wherein, the electrical generator provides power to a control system which controls the operation of the PRS.

12. An electrical generator system as claimed in any preceding claim wherein, the electrical generator provides power to a monitoring system which monitors the operation of the PRS.

13. An electrical generator system as claimed in any preceding claim wherein, the electrical generator provides power to a telemetry system which provides a communications link to the PRS.

14. An electrical generator system as claimed in any preceding claim wherein, the generator comprises a multi-piston high torque radial generator attached to a stepper motor.

15. An electrical generator system as claimed in any preceding claim wherein, the generated electricity is alternating current (AC).

16. An electrical generator system as claimed in any preceding claim wherein, the system further comprises a rectifier for converting AC to direct current (DC).

17. An electrical generator system as claimed in any preceding claim wherein, the system further comprises a battery for storing the generated DC.

18. An electrical generator system as claimed in any preceding claim wherein, the system further comprises an air return conduit for returning air that is exhausted by the radial generator back to the input of the air compressor for reuse so that filtration of new air is minimised, so extending the period for planned maintenance for air filter cleaning.

19. An electrical generator system as claimed in any preceding claim wherein, the electrical generator is housed in a cabinet which is outside the PRS.

20. An electrical generator system as claimed in any preceding claim wherein, the cabinet has an external non return valve and air intake together.21 . An electrical generator system as claimed in any preceding claim wherein, the cabinet has an air filter.

22. An electrical generator as claimed in any preceding claim wherein, the gas pump which is connected to the gas supply of the PRS via a conduit which diverts a portion of the gas to the gas pump which has sufficient volume to operate the gas pump.

23. A method for generating electricity for a pressure reduction station PRS, the method comprising:Connecting a gas pump to a gas supply of the PRS and which generates mechanical energy from the flow of gas through the pump;Using the mechanical energy to generate compressed air within a cylinder. Providing the compressed air to an electrical generator wherein the electrical generator generates electricity from the compressed air.

24. The method as claimed in claim 23 wherein, the gas pump is located inside the PRS within a hazardous zone “zone 0”.

25. The method as claimed in claim 23 or claim 24 wherein, the air compressor is located inside the PRS within a hazardous zone “zone 0”.

26. The method as claims in claims 23 to 25 wherein, the electrical generator is located outside the PRS “safe zone”.

27. The method as claims in claims 23 to 25 wherein, the gas pump is fed with high pressure input gas from a PRS input.

28. The method as claims in claims 23 to 27 wherein, the gas pump is located between a gas input valve and a regulator in the PRS.

29. The method as claims in claims 23 to 28 wherein, the electrical generator provides power to a control system which controls the operation of the PRS.

30. The method as claims in claims 23 to 29 wherein, the electrical generator provides power to a monitoring system which monitors the operation of the PRS and / or provides power to a telemetry system which provides a communications link to the PRS.31 . The method as claims in claims 23 to 30 wherein, the generator is an air powered pump attached to a stepper motor.

32. The method as claims in claims 23 to 31 wherein, the generated electricity is AC.

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