WO2011037487A1

WO2011037487A1 - Energy recovery actuating method and relating device

Info

Publication number: WO2011037487A1
Application number: PCT/RO2010/000001
Authority: WO
Inventors: Fililp Cojocaru
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-09-28
Filing date: 2010-02-22
Publication date: 2011-03-31
Anticipated expiration: 2012-03-28
Also published as: RO126135A2

Abstract

An energy recovery actuating method and a pressure gas actuating device accordingly, for cyclic upward and downward movements, utilized to lift a useful load together with a permanent weight, consuming less energy by recovering a part of the kinetic energy of the permanent weight during downward movement, having a pressure gas closed circuit, which comprises a pressure generator or a booster, a linear ^as actuator, a means which directs the fluid in one direction or in reverse, a gas accumulator and an auxiliary pressure generator. The energy drawn from electrical power grid is distributed over entire, up and down cycle, therefore is required less power and in consequence a smaller electrical motor size. Application fields: - Down hole oil or water pump sucker rod lift system, with front mounted geometry, class m lever system; - Lifting equipments for cyclic upward and downward movements, which carry significant loads and weights.

Description

10 000001

Energy recovery actuating method and relating device

BACKGROUND OF THE INVENTION

The invention discloses an energy recovery actuating method and a pressure gas actuating device accordingly, for cyclic upward and downward movements, utilized to lift a useful load together with a j>ermanent weight, consuming less energy by recovering a part of the kinetic energy of the permanent weight during downward movement, having a pressure gas closed circuit, which comprises a pressure generator or a booster, a linear gas actuator, a means which directs the fluid in one direction or in reverse, a gas accumulator and an auxiliary pressure generator.

The energy drawn from the electrical power grid is distributed over the entire up and down cycle, therefore is required less power and in consequence a smaller electrical motor size.

Application fields:

- Down hole oil or water pump sucker rod lift system, front mounted geometry, class III lever system;

- Lifting equipments for cyclic upward and downward movements, which carry significant permanent loads and weights.

PRIOR ART

A wide variety of the technical solutions for actuating oil pumping units are used, a lot of them having energy recovery and storing systems, due to up and down movements of the string rod which is considered as a permanent weight.

The majority of the solutions are hydraulically actuated, because is necessary to develop a large force to move the loads. A certain proportion of the kinetic energy of the permanent weight can be recovered during the downstroke of the rod string, stored and then released during upward movement, using pneumatic accumulators or/and flywheels.

The US patent no. 5,016,139 describes a hydraulic system, which includes a hydraulic fluid pump, a hydraulic cylinder, a pressure accumulator, a fluid valve 4/2 and a pilot-operated bypass valve. A hydraulic fluid valve is movable between a first position and a second position. In the first position, the valve directs fluid from the pump outlet to the hydraulic cylinder and from the accumulator to the pump inlet. In the second position the valve directs the fluid from the pump outlet to the accumulator and from the hydraulic cylinder to the pump inlet.

Some potential drawbacks of this system include a lot of pressure dynamic seals for the hydraulic pump and for the hydraulic cylinder that has long stroke, to move up and down the rod string. The system has not an auxiliary oil pump or similar device in order to replace the leaks of the fluid, therefore limiting operating time without stopping and refilling the installation with fluid.

Extending to a large scale of new technical solutions for actuating crude oil pumping units is limited because are necessary:

- Large oil reservoirs, breathing, filling, filtering systems;

- Nitrogen gas/oil diaphragm or piston accumulators, which use two fluids and consequently raise the frictions and lower overall efficiency;

- Complex and expensive dynamic seals and hydraulic parts;

- Large amount of investments and costly maintenance.

In the case of the conventional actuation for oil pumping units, the electrical motor is oversized, according to the maximum torque that is necessary to overcome the load, which varies according to a sinusoidal curve.

Considering as example the general case of a conventional pneumatic actuation in open circuit used for upward and downward movements, operating fluid - usually compressed air under pressure to up 12 bar, delivered by a compressor, which feeds a linear motor that lift a useful load and a permanent weight.

The permanent weight (or "dead weight") is a weight of the lifting equipment including all permanently attached machinery, as are the support and other accessories that bear the useful load and move upwardly with it, and downwardly without it.

During downward movement, the gas from the actuator is exhausted outside and the kinetic energy of the permanent weight is lost by friction generating heat, therefore the conventional pneumatic actuation has a lower efficiency and wastes the energy.

There are well known equipments that include hydraulic closed circuits, where motor outlet is connected directly to the pump inlet. These circuits have a charge pump that supplies cooled and filtered oil to the low pressure side and complete fluid leakage from circuit and drains, too. Compared with open circuit, closed circuit has an improved efficiency.

One aspect of the present invention is directed to an energy recovery actuating method, for cyclic upward and downward movements, having a pressure gas closed circuit, comprising a pressure generator or a booster, a linear gas actuator, a means which directs the fluid in one direction or in reverse, a gas accumulator and an auxiliary pressure generator.

An upward movement is accomplished due to a j*as existing in the accumulator haying a low pressure that is aspirated by a pressure generator or booster and delivered under higher pressure to a large chamber of a linear gas actuator, which lift a permanent weight with a useful load. The input work delivered by the pressure generator taken from grid power with the stored energy from the gas accumulator which act together to generate the lifting motion, are utilized to overcome the output work to lift a permanent weight with a useful load and also the work done by all resistive forces (including friction), which act against the lifting motion.

Arriving at the higher jioint of the stroke, the useful load is released and begins the downward movement with the permanent weight by connecting in reverse the suction of the pressure generator or booster which aspirates the gas from the large chamber of the linear gas actuator and discharge it with high pressure back into the accumulator. The input work delivered by the pressure generator taken from grid power with a part of the kinetic energy due to the permanent weight that act together to generate the downward motion, are used to compress the gas inside the gas accumulator charging it with recovered energy and also to overcome the work done by all resistive forces (including friction), which act against the downward motion.

Due to a pressure j>as closed circuit it is possible a continuous reuse and a recirculation of the gas under pressure as operating fluid from the accumulator to the pressure generator or booster and to the large chamber of the linear gas actuator and in reverse, without releasing exhaust gases to the outside.

The main advantage of this method consists in energy savings, owing to capture and store a part of the kinetic energy of the permanent weight during downstroke, and then release it during upstroke and spread the consumed energy by the pressure generator or booster's electrical prime motor from grid power as input work over entire cycle.

Other advantage is less power required from said pressure generator or booster's electrical prime motor, compared with conventional actuations, due to spreading of the energy drawn from grid power over entire cycle during upward and downward movements.

The larger is the ratio between permanent weight and useful load, the larger saving energy is. It is important not only to have a high general efficiency of the mechanism, but also to recover and use efficiently the potential or/and kinetic energy whenever is possible. In order to switch up and down movements, the pressure gas closed circuit has a means to change the gas flow direction at lower and upper position of the linear gas actuator stroke, a device comprising one or more elements which conduct the fluid from the accumulator to the pressure generator or booster suction and from the pressure generator or booster discharge to the large chamber of the linear gas actuator for upward movement and respectively in reversal mode, from the large chamber of the linear gas actuator to the pressure generator or booster suction and. from the pressure generator or booster discharge to the accumulator for downward movement.

It may be desirable to diminish the gas losses and leakage from gas closed circuit, so the linear gas driven actuator should have only one mobile joint for the piston cylinder type, or even none in case of diaphragm type. Also, another improvement can be a capsulated pressure gas generator or booster comprising an electric motor, which drives a compressor or booster; all sealed in a pressurized container similar to the hermetic compressors existing in refrigeration industry.

An auxiliary pressure generator is necessary to charge the pressure gas closed circuit with the gas under pressure jjrior to start operating in cycling mode, in upward and downward motion and also to compensate the gas leakage obviously present thru mobile and fixed joints during operation.

According to the present invention and to the energy actuating method described before, for exemplification is analyzed a pressure gas actuating device for upward and downward movements, used in conjunction with a down hole crude oil or water pump sucker rod lift system.

The pressure gas actuating device for upward and downward movements has a cinematic mechanism of class III lever system, front mounted geometry, as is specified in API Specification HE, very different from the conventional actuation for crude oil pumping units, which transforms the rotary motion of an electrical motor into a reciprocating motion of the string rod by a crank gear.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention. Whenever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 1 is a schematic and diagrammatic view of the pressure gas actuating device used for a down hole oil pump, related to one exemplary embodiment of this invention.

FIG. 2 is a schematic and diagrammatic view of the pneumatic actuating device used for a. down hole pumping unit, related to another exemplary embodiment of this invention.

FIG. 3 is a schematic and diagrammatic view showing the auxiliary nitrogen gas generator 17.0 in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

One exemplary embodiment of this invention, a pressure gas actuating device for upward and downward movements used for a down hole oil pump is shown having two main parts, a mechanism (items 1 ÷ 4) and a pressure gas closed circuit (items 4 ÷ 22), FIG. 1.

As shown in FIG. \, a mechanism which is part of the pressure gas actuating device includes a walking beam 1, a Samson Post bearing as fixed joint 2, a equalizer bearing as mobile joint 3, where is articulated the stem of a linear gas actuator 4. The linear gas actuator may be a diaphragm or a piston cylinder type. The permanent weight is formed by the walking beam 1, a horse head with mounted wireline hanger, a bridle block, a carrier bar, a polished rod and a rod string as it is in a conventional pumping unit (not shown in FIG. 1, can be seen in Petroleum Engineering Book, vol. IV, page 458).

By fastening the mobile joint bearing 3 and linear gas actuator 4 along the walking beam, 1 and by using different sizes of the linear gas actuator 4, a large range of strokes and forces for pumping units can be obtained to cover a lot of specific situations for well holes.

A double bistable solenoid pilot valve 5, which may be substitute for other type of control valves, is activated in position a to direct the gas from a gas accumulator 7 to a pressure gas generator or booster 6.1 (or 6.2) and further to a large chamber of the linear gas actuator 4 for the upward movement. For example, the pressure gas generator or booster 6.1 (or 6.2) can be reciprocating, screw, diaphragm, scroll or other compressor type. The pressure gas generator or booster 6.2 is similar to the hermetic compressors used in refrigeration industry, having a very good gas proof leaking.

For the downward movement the double solenoid pilot valve 5 commutes in position b and directs the gas from the large chamber of the linear gas actuator 4 to the pressure gas generator or booster 6.1 (or 6.2) and then back to the j*as accumulator 7.

The walking beam 1 is made up as a closed structure from welded steel sheets, see section A - A FIG. 1, and may be used also as a j*as accumulator working together or without the gas accumulators 7.

A pressure gauges 8 and 9 show outlet and inlet pressure of thejjressure gas generator or booster 6.1 (or 6.2) and a bypass valve 10 protects the pressure gas closed circuit against overpressure that may occur, due to an accidentally mechanical jam. Also, the electric motor that drives a compressor can be protected supplementary by specific electrical means.

A solenoid valve, two positions normal closed 11, separates low-pressure circuits from high-pressure_, circuits in the closed pressure gas circuit. When it is activated in open position b, it equalizes the pressures between suction and discharge of the pressure gas generator or booster 6.1 (or 6.2) in order to easy starting it, free of charge, and also prior to start operating, to charge the pressure gas closed circuit with gas underpressure.

A shut-off valve 13 and 15 are used to depressurize the pressure gas closed circuit and shut-off valves 12, 14 and 16 are used to pressure isolating different parts of the pressure gas closed circuit. The shut-off valve 16 will be mounted close to the mechanism to stop it, for easy accessibility, for repairing, maintenance or emergency purposes.

An auxiliary nitrogen pressure generator 17.0 as illustrated in FIG. 3, in a first variant can be used to charge and supply with nitrogen under pressure the pressure gas closed circuit, prior to start to operating, or in operating conditions when pressure decreases due to leakage of the nitrogen.

Instead of the auxiliary nitrogen pressure generator 17.0 can be used an auxiliary nitrogen gas cylinder 18.0, having same function, which is composed of a gas cylinder 18.1, a shut-off valve 18.2, a pressure gauge 18.3 and a pressure regulator 18.4, shown in FIG.l.

The composition and function of the nitrogen pressure generator is described further. The air is sucked thru filter 17.3 by a reciprocating, screw, diaphragm or scroll type compressor 17.1, driven by an electric motor 17.2, compressed and sent to the cooler 17.4, whereby the nitrogen is separated from air passing thru nitrogen membrane generator 17.5 and finally is stored in the receiver 17.7. The nitrogen pressure stored in the receiver is read on gauge 17.8.

A check valve 17.6 prevents gas to flow back from the receiver into the nitrogen membrane generator and the water trap 17.10 collects and ejects condensed water from the nitrogen gas receiver 17.7, which is protected from overpressure by a safety valve 17.9. 0001

The compressor 17.1 is automatically switched on by a pressure switch 17.11, until the maximum_^ pressure existing inside the nitrogen j>as receiver 17.7 reaches a set value which is far higher than a minimum operating pressure existing in the pressure gas closed circuit.

A shut-off valve 17.14 in open position helps the compressor 17.1 to start easy, without pressure on his outlet side.

A controller (not shown) receives input signals from the limit switches, pressure transmitter 19 and temperature transmitter (not shown) located on the electrical motor or pressure gas generator, in order to generate an output control signal used to shut down the electrical motor, to protect pneumatic actuating device from an accidental failure.

The controller also compares the value of the minimum operating pressure from a pressure transmitter 19 located on compressor or booster suction circuit with a minimum set value that corresponds to a proper operating condition of the gas actuating device. When minimum operating pressure drops below a minimum set value, due to a shortage of the nitrogen gas in the pressure gas closed circuit, the controller command the 2/2 directional control valve 17.12 in position b to open the passage into the closed circuit of the nitrogen gas stored under high pressure inside the nitrogen receiver 17.7 thru a pressure regulator 17.13, which reduces it to a minimum set value.

The pressure regulator is used to keep under control the minimum operating pressure that may drops below a minimum set value, recharging periodically and automatically the pressure gas closed circuit with gas pressure during downward movement, without stopping the operation when the operating gas is extracted by the suction of the pressure generator or booster from the large chamber of the linear gas actuator.

A gas cooler 20 is necessary to cool the compressed hot gas coming from the pressure generator.

A check valve 21 is connected between suction and discharge of the pressure generator, or booster, to discharge rapidly the gas pressure coming from the suction circuit, when double bistable solenoid pilot valve is commuted at lower or at upper position of the linear gas actuator.

In order to improve the cooling conditions and save the energy, the pressure generator has an additional cooler 22, which is a shell and tube heat exchanger type, where the cold stream is just pumping fluid, crude oil or water and the hot stream is compressed gas.

Another exemplary embodiment of this invention which is a pneumatic actuating device used for a down hole pumping unit, or for actuating other various mechanisms having significant permanent weight shown in FIG. 2, is a simplified variant of the pressure gas actuating device as illustrated in FIG. 1. This pneumatic actuating device operates substantially in the same manner as the arrangement of FIG. 1 described above, except that has not an auxiliary nitrogen pressure generator 17.0 or an auxiliary nitrogen gas cylinder 18.0 and may be used with air as operating gas, usually but not limited, under pressure up to 12 bar.

PREP ARATION FOR OPERATION

1) Preparation for operation of the pressure gas actuating device used for a down hole oil pump with an auxiliary nitrogen pressure generator 17.0, or an auxiliary nitrogen gas cylinder 18.0, FIG. 1, related to one exemplary embodiment of this invention.

Usually, this variant uses nitrogen gas under high pressure (over 12 bar). In order to charge the pressure gas closed circuit with nitrogen gas under a predetermined pressure, prior starting to operate, the shut-off valves 12, 14 and 16 are in open position, shut-off valves 13 and 15 in closed position, solenoid valves 11 and 17.12 actuated in open position b, FIG. 1. The auxiliary nitrogen pressure generator 17.0, which extracts and compresses the nitrogen gas from the atmosphere, fills the entire gas circuit, including gas accumulator 7 in a preparatory stage of operation, allowing starting operation of a linear gas actuator 4 from that state. The auxiliary nitrogen pressure generator 17.0 will deliver nitrogen gas until it. reaches a predetermined charge pressure necessary for proper operating as mentioned above.

After reaching the predetermined charge pressure in the pressure gas closed circuit, the auxiliary nitrogen pressure generator 17.0 stops and the solenoid valves 11 and 17.12 are de-energizing in closed position a.

Upon starting the electric motor to drive thej>ressure gas generator or booster 6.1 (or 6.2), each limit switch produce alternatively an electrical signal to the solenoids of the solenoid pilot valve 5 at the ends of the stroke and consequently commutes it in positions a or b. Accordingly, the fluid pressure drive circuit of the present invention can operate the linear gas actuator 4 automatically, for upward and downward movements.

After each shut down of the pressure gas actuating device, before starting operating, it is necessary to have an equal pressure to the inlet and outlet of the pressure gas generator or booster 6.1 (or 6.2), identical with the predetermined charge pressure mentioned before, therefore the shut-off valves 12, 14 and 16 are in open position, shut-off valves 13 and 15 in closed position and the solenoid valves 11 in open position b.

In resting position of the pressure gas actuating device, the predetermined charge pressure is higher than the minimum set operating pressure, which is the gas pressure aspirated by the pressure generator or booster from the large chamber of the linear gas actuatpr during downward movement.

2) Preparation for operation of the pneumatic actuating device used for a down hole pumping unit, without an auxiliary nitrogen pressure generator 17.0 or an auxiliary nitrogen gas cylinder 18.0, related to another exemplary embodiment of this invention, FIG. 2

Usually, this variant uses air under pressure up to 12 bar, with pressure gas generator, or booster 6.2. For the beginning, the pressure gas closed circuit (including the gas accumulator 7) is charged with air under a predetermined charge pressure. In this respect, the shut-off valves 13, 14 are in open position, shut-off valve 12 in closed position, solenoid valve 11 in open position b. Instead of the solenoid valve 11 can be used a shut off valye, having same role. The pressure gas generator 6.2 sucks air from atmosphere, compresses and sends it under pressure in the pressure gas closed circuit until it reaches a predetermined charge pressure. After reaching the predetermined charge pressure in the pressure gas closed circuit, the pressure gas generator 6.2 is stopped, the shut-off valve 13 is actuated in closed position, the shut-off valve 12 in open position and solenoid valve 11 de-energized in closed positions .

Upon starting the electric motor to drive the pressure gas generator 6.2, each limit switch produces alternatively an electrical signal to the solenoids of the solenoid pilot valve 5 at the ends of the stoke and consequently commutes it in positions a or b. Accordingly, the, fluid pressure drive circuit of the present invention can operate the linear gas actuator 4 automatically, for upward and downward movements. During o eration it is not possible to fill the pressure gas closed circuit with pressurized air, but only when using an auxiliary air compressor.

If the pressure gas closed circuit uses low-pressure air below 12 bar, without the auxiliary nitrogen pressure generator 17.0, or the pressure nitrogen cylinder 18.0, it can operate also as in open classical circuit. In this case, the shut off valve 12 is closed, the valves 13, 14 are open and the solenoid valve 11 de-energized in closed position a. The gas accumulator 7 ensures a minimum pressure to commute the solenoid pilot valve 5 in positions a or b, when corresponding solenoid is activated alternatively by the limit switches (not shown) , in order to actuate downward or upward movement the piston and stem of the linear gas actuator 4, together with the useful load.

ADVANTAGES

Comparing with actual conventional and unconventional actuation of the pumping units, the, energy recovery actuating method and a pressure gas actuating device according to the present invention has numerous advantages.

- reduced complexity, size, footprint, weight and cost;

- easy to make, transport, assemble and maintain;

- high reliability, due to a reduced number of items, moving parts and dynamic seals;

- eliminates oil spillage, the operating fluid is not toxic or polluted, the impact for the, surrounding environment is very low, the technology which is used is ecological, practically it's not any kind ofpollution with noxious substances;

- the cost of the operating fluid (inert gas - nitrogen for high pressures, or air used exclusively, is one of the lowest, the fluid no needs reconditioning, collecting or replacement_^ only completing the fluid leakage;

- the use of the nitrogen as inert gas instead air prevent plasties and rubber oxidation, does not corrode internal pressurized parts and improves the permeability diminishing gas leakage,

- the pressure nitrogen generator has low capacity, because it is used only to charge with nitrogen the installation prior to initially start and to replace inevitable gas leakage;

- the walking beam used also as gas accumulator operating together or without the gas, accumulators, is made up as a closed structure from welded steel sheets and lower the weight and cost of the pneumatic actuating device;

- less energy consumption comparing with conventional pumping units, due to the recovery of a part of the permanent weight from the sucker rod (according to the ratio between permanent weight and useful load);

- energy savings using an additional cooler, tube heat exchanger type, due to warm up of the pumping fluid, crude oil or water, used as a cold stream and the hot stream being compressed gas;

- the energy consumed from grid power as useful work is spread evenly over the entire cycle (upward and downward movements), therefore smaller size for prime electric motors can be used;

- it prevents power penalties from utility companies by avoiding current peaks during start-up and because there are no load peaks ;

- improved power factor (cos φ), no need to carry out expensive actions to increase power factor;

- easy and smooth start under load, a smooth start-up at low speeds eliminating current and torque peaks, no shocks provided;

- reduced C02 and other noxious gases, because of lower installed power compared with conventional pumping units which can be used in similar conditions;

- reduced implementation costs for the maintenance and advanced automation of the pneumatic actuating device and whole unit pump, according to local requirements;

- the controller - operating as master control - can be used in conjunction with the monitoring electronics to monitor various operating states, errors and service intervals like oil level, air outlet temperature, pressure relief, temperature, admission pressure, various maintenance intervals;

- easy to implement remotely control;

- improved safety, reduced technical accidents due to different embedded safety systems; - using various sizes of the standardized linear motors, joined along the walking beam in equalizer bearing at different distance from the Samson Post bearing, a large numbers of combinations of the strokes, speed and polished-rod load can be obtained, to cover a wide range of pumping units;

- high reliability, easy to maintain, reduced spare parts, only a few moving parts and consumables;

- may be used in dangerous explosion area;

- reduced cost and investments to adapt and implement to existing sucker rod artificial lift method;

- no need of large, heavy and complex reservoirs for operating fluid, also no need for systems for filtering, filling, breathing, testing hydraulic oils.

Claims

Energy recovery actuating method and relating device Claims What I claim is:

1. An energy recovery actuating method, for cyclic upward, and downward movements, having a pressure gas closed circuit, comprising a pressure generator or a booster, a linear gas actuator, a means which directs the fluid in one direction or in reverse, a gas accumulator and an auxiliary pressure generator, which accomplishes:

an upward movement where a low pressure gas, existing in said accumulator is aspirated by th said pressure generator or booster and delivered under higher pressure to a large chamber of said Jinear gas actuator which lift ihe permanent weight with a useful load, thereby the input work delivered by said pressure generator taken from grid power with the. stored, energy from said gas accumulator which act together to generate the lifting motion, are utilized to overcome the output work, to lift a permanent weight with useful load and also the work done by all resistive forces (including friction), which act against the lifting motion;

a release of the useful load at the higher point of the stroke;

a downward movement with permanent weight by connecting in reverse the suction of said pressure generator or booster which aspirates the gas from said large chamber of said linear gas actuator and discharge it with high pressure back into said accumulator, thereby the input work delivered by said pressure generator taken from grid power with a part of the kinetic energy from the permanent weight that act together to generate the downward motion, are used to compress the gas inside said gas accumulator charging it with recovered energy and also to overcome the work done by the resistive forces (including friction), which act against the downward motion;

a continuous reuse and a recirculation of the gas under pressure as operating fluid from said accumulator to said pressure generator or booster and to the large chamber of said linear gas actuator and in reverse, without releasing exhaust gases to the outside;

an energy saving owing to capture and store a part of the kinetic energy of tlie permanent weight during downstroke, and then release it during upstroke; less power required from said pressure generator or booster's electrical prime motor, compared with conventional actuations, due to spreading of the consumed energy drawn from grid power over entire cycle during upward and downward.movements; a means to change the gas flow direction at lower and upper position of said linear gas actuator stroke carried out by a device comprising one or more elements which conduct the fluid from said accumulator to said pressure generator or booster suction and from said pressure generator or booster discharge to a large chamber of said linear gas actuator for upward movement and respectively in reversal mode, from a large chamber of said linear gas actuator to said pressure generator or booster suctio and from said pressure generator, or booster discharge to said accumulator for downward movement;

a reduction of the gas losses and leakage from said pressure gas closed circuit using only one mobile joint for piston cylinder type, or even none in case of diaphragm type for said linear gas actuator and also using a capsulated pressure generator or booster comprising an electric motor which drives a compressor or booster, all sealed in a pressurized container similar to the hermetic compressors existing in refrigeration industry;

a charging of said pressure gas closed circuit with gas under pressure prior to start operating and also to compensate gas leakage obviously present thru mobile and fixed joints during operation by an auxiliary pressure generator ;

2. An energy recovery gas actuating device, with operating fluid nitrogen, for cyclic upward and downward movements, for down hole oil or water pump sucker rod lift system, manufactured according to the claim 1, comprising:

a mechanism having cinematic of class ΙΠ lever system, front mounted geometry, as is specified in API Specification 1 IE, which includes:

a walking beam with horsehead (1), which oscillates articulated in

a Samson Post bearing as fixed joint (2);

an equalizer bearing as mobile joint (3), with joined stem of the linear gas actuator (4), piston cylinder or diaphragm type;

a bridle block, a carrier bar, a polished rod, a rod string (including also walking beam) as permanent weight and a pumping fluid as useful load; a pressure gas closed circuit, including: a pressure gas generator or booster. (6.1), for example a reciprocating, screw, diaphragm or scroll type compressor,- to compress an operating gas, driven by an electric motor, both preferably sealed in a-pressurized container (6.2);

one or more gas accumulators (7) storing the energy of the gas under pressure as part of the kinetic energy coming from the permanent weight in the downward movement and releasing it in the upward movement, switehably connectible to suction or to discharge of said pressure generator or booster, through a double bistable solenoid pilot valve (5 with two coils activated alternatively by the limit switches for upward and downward movement;

a pressure gauge (8) to show maximum discharge pressure of said pressure generator or booster;

a pressure gauge (9) to show minimum suction pressure connected with the suction of said pressure generator;

a bypass valve (10) to limit the overpressure in said pressure gas closed circuit; a solenoid valve, two -positions, normal closed (11), activated in open position equalizes the gas pressure between suction and discharge of said pressure gas generator or booster in order to easy starting it, free of- charge, and also prior to start operating, to charge said pressure gas closed circuit with nitrogen gas under pressure, by

an auxiliary nitrogen pressure generator (17.0), which is used also to supply with nitrogen under pressure said pressure gas closed circuit in operating conditions when pressure decreases due to leakage of the nitrogen gas, or by an auxiliary nitrogen gas cylinder (18.0) instead, having same function, composed of a gas cylinder (18.1), a shut-off vah e (18.2), a pressure gauge (18.3) and a pressure regulator (18.4);

a number of the shut off valves (12÷16) in order to pressure isolating different parts of the said pressure gas closed circuit;

a gas cooler (20) connected to the discharge of the said pressure gas generator or booster;

a check valve (21) connected between suction and discharge -of said pressure generator or booster, to discharge rapidly the gas pressure coming from suction, when said double bistable solenoid pilot valve is commuted at lower or at upper position of the stroke of said linear gas actuator; an additional gas cooler (22), which is a shell and tube heat exchanger type, where the cold stream is just the pumping fluid, crude oil or water and the hot stream is compressed gas, connected to the suction or discharge of said pressure generator, in order to save energy;

a pressure transmitter (19) located on said pressure gas generator or booster (6.1 or 6.2) suction circuity

a temperature transmitter (not shown) located on said electrical motor or . said pressure gas generator or booster (6.1 or 6.2);

a controller (not shown) which receives input signals from the limit switches, pressure transmitter (19) and temperature transmitter;

3. An energy recovery gas actuating device, as defined in claim 2, wherein said walking beam is made up as a closed structure from welded steel sheets, which may be used also as gas accumulator working together or without other said gas accumulators;

4. An energy recovery gas actuating device, as defined in claim 2, wherein said mobile joint bearing and said linear gas actuator can be fixed along said walking beam and also using different sizes of said gas linear actuator, to obtain a large range of strokes and forces for said pumping units to cover a lot of specific field situations for well holes;

5. An energy recovery gas actuating device, as defined in claim 2, wherein said auxiliary nitrogen pressure generator comprises:

an air filter (17.3) wherein passing air is sucked and compressed by

a reciprocating, screw or diaphragm type compressor (17 1) driven by an electric motor (17.2) automatically switched on by

a pressure switch (17.11), until the maximum pressure existing inside

a nitrogen gas receiver (17.7) reaches a set value which is far higher than a minimum operating pressure existing in said pressure gas closed circuit;

a pressure gauge (17:8) connected to said receiver;

a safety valve (17.9)-to protect from overpressure said nitrogen receiver;

a water trap (17.10) that collects and ejects condensed water from said nitrogen gas receiver,

a cooler (17:4) to cool compressed air exhausted from said compressor which is send thru

a nitrogen membrane generator (17; 5) where nitrogen is separated from air and stored in said nitrogen gas receiver and retained inside by a check, valve (17.6) which prevent gas to flow _. back into the nitrogen membrane generator;

a directional control valve, two positions, normal closed (17.12);

a pressure regulator (17.13) which reduces the higher pressure from said receiver to a minimum set value necessary to feed automatically said pressure gas closed circuit, without stopping the operation;

a shut÷off valve (17.14) commuted in open position helping said compressor to start easy, without pressure on his outlet side;

6.. An energy recovery actuating device, as defined in claim 2, wherein said controller compares the value of the minimum operating pressure from said pressure transmitter (19) with a minimum set value that corresponds to a proper operating condition of the said energy recovery actuating device, so that when operating pressure drop below the minimum set value, said controller commands said directional control valve (17.12) located in said auxiliary nitrogen pressure generator to open the passage of the nitrogen gas from said nitrogen receiver to said pressure gas closed circuit until it reaches the necessary minimum set value, thereby the recharge of said pressure gas closed circuit with gas pressure is accomplished periodically and automatically without stopping the operation;

7. An energy recovery actuating device, as defined in claim 2, wherein said controller receives input signals from said limit switches, said pressure and temperature transmitters, in order to generate an output control signal to shut down said electrical motor to protect said energy recovery actuating device from an accidental failure;

8. An energy recovery actuating device, as defined in claim 2, a simplified version, which uses air as operating gas and has not an auxiliary nitrogen -pressure generator (17.0) or auxiliary nitrogen gas cylinder (18.0) but only an auxiliary air compressor may be used with.