WO2015083095A1

WO2015083095A1 - Energy recovery system, and method thereof

Info

Publication number: WO2015083095A1
Application number: PCT/IB2014/066550
Authority: WO
Inventors: Sergio BOGGE
Original assignee: Re.Mac.Ut. S.R.L.
Priority date: 2013-12-04
Filing date: 2014-12-03
Publication date: 2015-06-11
Also published as: ITTO20130989A1

Abstract

The present invention relates to an energy recovery system (1,10), and to the relevant method, wherein there are provided at least one variable displacement pump/compressor unit (3,30), at least one accumulator (4,40), at least one electric motor (5,50), at least one generator (7,70) and at least one control unit (6,60), said system (1,10) being connected to at least one electric appliance (2,2A',2A",..., 2Aⁿ,20) only through the electric supply network (9,90) and in case to another control system(s) for exchanging data useful to the adjustment. The present invention is preferably, but not exclusively, used to realize an electric energy recovery system (10) for a plant equipped with a heave compensator (20) in the field of the off-shore applications.

Description

'Energy recovery system, and method thereof

DESCRIPTION

Technical Field

The present invention relates to a system, and to the method thereof, for the energy recovery. Precisely, the present invention relates to a system, and to the method thereof, for the energy recovery from an electric network.

More precisely, the present invention relates to a system, and to the method thereof, for the electric energy recovery in cases where large fluctuations of power required to the electric supply network occur.

Even more precisely, the present invention relates to a system, and to the method thereof, for the electric energy recovery to be employed in the field of the off-shore applications.

The present invention is preferably, but not exclusively, used to realize an energy recovery system for a plant equipped with heave compensation.

Known Prior Art

When managing plants in the industrial, naval, shipbuilding and similar fields, situations usually occur wherein large variations of the power required by the appliances connected to the electric supply network are present; many of these applications are cyclical, for example when a load is raised and lowered at more or less regular intervals, during which periods when a very high power is required to the electric network are alternated with periods during which an as much high power is generated.

Whenever a machine is subjected to time-varying loads, impulsive power requests very different from the required average power are generated; generally, therefore, in such conditions, the power supply network, including the electric energy generators, must be sized so as to meet the requirements of instantaneous maximum power required by a given operation.

In some cases, for example where high masses or accelerations are present, the power supply system could be very oversized with respect to the required average power; in extreme cases, the power regenerated by the appliances could exceed the power consumed by other appliances connected to the same electric supply network, even forcing to dissipate the energy generated in excess. Examples of such plants are the lifting and handling systems (such as cranes, robots and similar), the plants with considerable unbalanced rotating masses and the tracking systems subjected to strong accelerations and decelerations (such as the lifting systems with heave compensation).

Particularly in the field of the off-shore applications, namely on ships and floating platforms, the available power is limited and even more limited is the power generated by the appliances during the regenerative phases that the on-board network can receive, because it results difficult to be dissipated or reusable.

The generation of high powers involves a considerable use of space on board the naval vessels and a consequent increase in costs; the increase of spaces and costs obviously represents an important problem, which has then led to the development of new systems for the energy recovery.

The importance of the energy recovery is also strongly felt more in general when very high instantaneous powers are required, due to the cost of energy that, especially in recent years, has considerably increased.

An example of a system and a method for the recovery of energy, specifically of hydraulic energy, is shown in the International Patent application published with the No. WO 2011/145947 Al, which highlights that the dissipation of all the energy in excess as heat, particularly in the case of high powers, is very heavy; the system according to said application intends, therefore, to solve the problem of dissipation of energy as heat by suggesting the recovery and the use of the recovered energy in a subsequent operation, and thus making possible to reduce the installed power of the whole power generation plant; said system, in particular, is associated with a heave compensator.

The system according to the aforesaid application comprises two hydraulic machines connected to an electric motor; the former of said two hydraulic machines is hydraulically connected to the actuator of a system for lifting/lowering the load and the latter of said two hydraulic machines, precisely a variable displacement pump/compressor unit, is hydraulically connected, through a valve, to a hydraulic accumulator or to the aforementioned actuator of a system for lifting/lowering the load; by adjusting the displacement of the latter hydraulic machine, it is possible to store in the accumulator the energy that otherwise would be dissipated as heat, for giving it back to the appliance afterwards. Depending on the lifting of the load - which operation absorbs energy - or on the lowering of the same load - which operation generates energy - the hydraulic accumulator delivers or receives energy from the actuated appliance.

The teaching of this document however, being limited to a mechanical/hydraulic system and specifically providing that the two hydraulic machines are mechanically connected to each other, allows a very low overall yield and limits the use thereof only to those machines wherein the end appliance is a hydraulic one.

Objects and Brief Description of the Invention

The present invention, starting from the notion of the drawbacks and deficiencies of the known prior art, intends to overcome them.

In particular, the present invention intends to solve and eliminate the problems present in the prior art solutions and specifically:

- the direct dependence of the energy recovery system from the (hydraulic) actuated machine,

- the need to have a hydraulic final appliance,

- the need to perform adjustments and calibrations to adapt the system to the operating conditions of the moment (masses to be moved, velocities and accelerations),

- the low overall yield of the plant.

The present invention aims, therefore, at:

- powering any type of appliance, particularly requiring high powers and/or high instantaneous power peaks,

- recovering and reusing the energy in excess,

- avoiding adjustments and calibrations to adapt the system to the operating conditions of the moment, and

- increasing the overall yield of the plant.

It is, therefore, the main object of the invention to provide a system, and the relevant method, allowing to:

- store and release in the electric supply network large amounts of energy in short times, and therefore large instantaneous powers, regardless of the appliances that generate the power variation requested to the electric network;

- make available the stored energy back to the electric supply network, specifically in case of high instantaneous power peaks; - realize an energy accumulation-release system that does not require expensive and complicated adjustments to adapt it to the different operating conditions; and

- improve the overall yield of the energy accumulation system.

The invention provides, therefore, an electric primary energy system, and the relevant method, that thanks to the provision of an accumulation system of pressurized fluid, for example a variable displacement pump/compressor unit actuated by an electric motor and connected to an accumulator (hydraulic in case the fluid is a liquid), allows to achieve the objects set out above.

More specifically, the present invention provides a system, and the relevant method, that provides only the connection to the electric supply network.

Even more precisely, the present invention provides a system, and the relevant method, that does not provide mechanical, hydraulic or electric connections between the at least one appliance and the energy recovery system.

The system, and the relevant method, according to the present invention can be briefly defined as an electric energy accumulator that temporarily makes use of pressure accumulators, to ensure instantaneous powers that the electric generation system is not able to provide.

The present invention is therefore suitable for the realization of an energy recovery system in combination with equipment for heave compensation in the field of the off-shore applications, but it can also be employed in all those applications where strongly and cyclically varying in time powers are requested to the electric network in order to be able to size the generators for the consumed average power rather than for the instantaneous peak power.

A not least object of the present invention is to provide an energy recovery system, and the relevant method, cheap, easy to be realized, precisely operable, highly reliable and accurate. In view of these objects, the present invention provides a system and the relevant method having the features of the appended claims 1 and 7, respectively, to which reference is made for sake of brevity of exposition; furthermore, the present invention also provides the use of said system and method specifically for heave compensators having the features of the appended claims 5 and 6, respectively, to which reference is made for sake of brevity of exposition. It is, therefore, a first object of the present invention, in case independent and autonomously usable with respect to the other aspects of the invention, a system, and the relevant method, for the energy recovery as electric energy by using an accumulation system that is not electric but it is based on a pressurized fluid.

It is, therefore, another object of the present invention, in case independent and autonomously usable with respect to the other aspects of the invention, a system, and the relevant method, for the energy recovery as electric energy in the off-shore field and specifically in combination with heave compensators.

Further detailed advantageous technical features of the system and of the relevant method as well as their specific application for heave compensators, according to the present invention, are described in the corresponding dependent claims.

The aforesaid claims, hereinafter defined, are intended to be as an integral part of the present description.

As it will result evident from the following detailed description, the system and the relevant method according to the present invention have important advantages in particular with respect to systems recovering hydraulic energy.

Description of the Figures

The present invention, together with the objects and advantages thereof, will become more evident from the following detailed description, relating to preferred embodiments of the system and the method thereof herein exclusively claimed, given by way of indicative and illustrative, but not-limiting, example, with reference to the appended drawings, which are given only by way of example too, in which:

Fig. 1 is a schematic representation of the energy recovery system according to the present invention;

- Fig. 1A is a schematic representation of a variant, comprising a plurality of appliances, of the energy recovery system of Fig. 1;

Fig. 2 is a flow diagram showing the method of the energy recovery system according to the present invention; and

Fig. 3 is a schematic representation of the energy recovery system according to the preferred embodiment of the present invention, in which said system is combined with a heave compensator. These drawings show different aspects and embodiments of the present invention and, if appropriate, similar structures, components, materials and/or elements are denoted by the same reference numbers in different figures.

Detailed Description of the Invention

While the invention is susceptible of different modifications and alternative constructions, some embodiments thereof will be described in detail hereinbelow, in particular by means of some illustrative examples.

It should be understood, however, that there is no intention to limit the present invention to the described specific embodiments but, on the contrary, the invention intends to cover all the modifications, alternative constructions and equivalents that fall within the scope of the invention as defined in the appended claims.

In the following description, therefore, the use of "for example", "etc." and "or" denotes non-exclusive alternatives without limitation, unless otherwise indicated; the use of "also" means "among, but not limited to", unless otherwise indicated; the use of "includes / comprises" means "includes / comprises, but not limited to", unless otherwise indicated.

With reference to Figure 1, the general embodiment of the present invention with application to a generic appliance is described, while in Figure 1A the same general embodiment of the present invention is shown in the variant providing the application thereof to a plurality of generic appliances; these figures show two variants of the present invention and, where appropriate, reference numbers showing identical structures, components and/or elements are denoted by the same reference numbers in the two different figures.

All the electric networks, to which appliances inducing strong cyclical variations of the required power (such as, for example, lifting systems, presses, etc.) are connected, can advantageously benefit from the energy recovery system according to the present invention; these appliances usually require powers whose oscillation ranges from few kW, for example from 5 kW, to tens MW, for example to 50 MW and more, with oscillation periods from few seconds, for example 2 seconds, to hundreds seconds, for example 600 seconds.

Consequently, the energies to be stored can be considerable and the sizing of the pressure accumulators, of the electric motors and of the pumps/compressors units of the energy recovery system depends on said energies.

More generally, the energy recovery system according to the present invention acts so as to maintain as constant as possible the power absorbed by the generation system, compensating the power peaks required by the network to the generation system when this power exceeds the maximum set value and accumulating energy when the power required to the generation system is lower than the same maximum set value; in particular, the predetermined threshold value of the maximum average power ranges between few kW and tens MW, preferably between 5 kW and 50 MW and more, even more preferably between 10 kW and 20 MW.

The following description shows an energy recovery system with a single set of motor - pump/compressor - pressure accumulator - tank; it is evident that the same system can consist of an indefinite number of modules with more motors, pumps/compressors, pressure accumulators and tanks connected to each other in different combinations.

The energy recovery system shown in Figure 1, denoted as a whole by the reference number 1, comprises a variable displacement pump/compressor unit 3 fed with a fluid (a gas such as, but not exclusively, air or nitrogen or a liquid such as, but not exclusively, oil or water) optionally contained in a tank 8.

Preferably, said pump/compressor unit 3 is of the variable displacement type with proportional displacement control; preferably, said variable displacement pump/compressor unit 3 has an operating pressure depending on the used fluid, on the required dynamics and on the amount of energy to be stored as well as on the currently available technology (approximately, the pressures can vary from few units to several hundreds bar).

Said variable displacement pump/compressor unit 3 is connected to an accumulator 4, preferably a pressure accumulator; said accumulator 4 can be, for example, of the oleodynamic type, but different fluids such as water, gas and the like could be similarly used.

Preferably, said accumulator 4 is of the bag, piston or membrane type when a liquid is used or it is a simple pressurized tank if using a gas.

Said variable displacement pump/compressor unit 3 is connected through a first duct 34 to said pressure accumulator 4 and in case through an optional second duct 38 to said tank 8. Said variable displacement pump/compressor unit 3 is further connected to an electric motor 5 that, in turn, is connected to an electric supply network 9 powered by a generation system 7.

Said electric motor 5 is suitable to actuate said variable displacement pump/compressor unit 3 and it is also suitable to be powered through the electric supply network 9. Said electric motor 5 and said generator 7 are of the type usually used in the industrial, naval, shipbuilding and similar fields.

Said variable displacement pump/compressor unit 3 is further connected to a control unit 6 that, in turn, is connected to the electric supply network 9 too; specifically, said control unit 6 is operatively connected to said variable displacement pump/compressor unit 3 and it is suitable to vary the displacement thereof.

Preferably, said control unit 6 comprises a processor able to detect the load on the electric supply network 9 and to consequently adjust the energy recovery system 1 so that it absorbs or delivers energy to the electric supply network 9.

Finally, an appliance 2 is connected to the same electric supply network 9 that powers said electric motor 5 and said control unit 6; the appliance 2 can be anyone among those listed above, taking into account that such list should not be regarded as exhaustive of all the possible appliances that can be combined to the energy recovery system 1 according to the present invention.

As shown in Figure 1A, a plurality of appliances 2A',2A",..., 2Aⁿ connected to the electric supply network 9 that powers said electric motor 5 and said control unit 6 can be provided; the appliances 2A',2A",..., 2Aⁿ can be any combination among those listed above, taking into account that such list should not be regarded as exhaustive of all the possible appliances that can be combined to the energy recovery system 1 according to the present invention.

The supply network 9 is connected to at least one sensor S2 (Fig. 1) or S2A (Fig. 1A) for detecting an energy variation available on the electric supply network 9 to which said electric motor 5 is connected; the term "sensor" is herein intended to mean both any device that detects and measures an input physical quantity and provides an output signal for the purpose of measurement or control of the system in which it is used, and any system installed or eventually already existing system that provides to the control unit of the appliance/appliances the necessary information on the electric load.

Said control unit 6 is arranged to increase/reduce the displacement of said variable displacement pump/compressor unit 3 when an excess or a request of energy occurs, respectively, by said appliance 2 or by said plurality of appliances 2A',2A",..., 2Aⁿ.

In particular, said control unit 6 is arranged for

increasing the displacement of said variable displacement pump/compressor unit 3 when said sensor S2,S2A detects that the power required to the electric supply network 9 is lower than the set maximum power threshold, so as to absorb more electric power from the electric supply network 9 through the electric motor 5 and to accumulate part of the energy absorbed by the electric motor 5 in the pressure accumulator 4, and

- reducing the displacement of said variable displacement pump/compressor unit 3 until it acts as a motor when said sensor S2,S2A detects a power request from the electric supply network 9 higher than the set maximum power threshold, so that the pressure accumulator 4 delivers energy to the variable displacement pump/compressor unit 3 that thus acts as a motor, while the electric motor 5 acts as an electric generator releasing electric energy to the electric supply network 9.

Said power thresholds may be dynamically changed depending on the operating conditions; signals for the adjustment thereof, as aforesaid, may also be sent by the control systems of the involved single appliances.

More precisely, said control unit 6 proportionally adjusts the displacement of the pump/compressor unit 3 so as to maintain as constant as possible the power absorbed from the electric supply network 9 by limiting the oscillations thereof at around the desired average value.

Even more precisely, said control unit 6 is arranged to increase the displacement of said variable displacement pump/compressor unit 3 when said sensor S2,S2A detects an increase of power available on the electric supply network 9 higher than a predetermined value that we will indicate as "maximum average power" and said control unit 6 is arranged to reduce the displacement of said variable displacement pump/compressor unit 3 when said sensor S2,S2A detects a request of power from the electric supply network 9 higher than the same "maximum average power" value; said "maximum average power" ranges between few kW and tens MW, preferably it ranges between 5 kW and 50 MW and more, even more preferably it ranges between 10 kW and 20 MW.

Said sensor S2,S2A is connected to said electric supply network 9 so that to detect the electric power required to the electric supply network 9 from said electric appliance 2 connected to the electric supply network 9 or from said plurality of appliances 2A',2A",..., 2Aⁿ connected to the electric supply network 9, respectively.

Said sensor S2,S2A may be replaced by a feedback of the control system of the appliance 2 or of the plurality of appliances 2A',2A",..., 2Aⁿ. It is worthy herein to underline that the system according to the present invention does not provide mechanical and/or hydraulic connections and it can even not provide electric connections between the appliance 2 or the plurality of appliances 2A'_/2A"_/..._/ 2Aⁿ and the energy recovery system 1 since the only strictly necessary common connection is the electric supply network 9; a connection to the control system of the appliance 2 or of the plurality of appliances 2A'_/2A",..._/ 2Aⁿ could be provided. The system according to the present invention can be defined as an electric energy accumulator temporarily using pressure accumulators in order to ensure powers that the electric generators are not able to achieve. For clarity's sake, in Figures 1 and 1A only the essential functional components of the system 1 are shown, while it is understood that other components may be provided, such as valves, pressure gauges and similar components, suitable for controlling and adjusting the system of the invention.

The described system 1 allows to recover electric energy and to make it available for a subsequent use, as it is clarified hereinafter.

With reference to Figure 2, the two possible operative cycles of the system 1 are shown and, more precisely, the method for energy recovery using the system 1 is shown, the steps of said method being:

i. detecting, by means of at least one sensor S2,S2A or of the connection to the control system of the appliance 2 or of the plurality of appliances 2A',2A",...,2Aⁿ the power supplied by an electric supply network 9 (step 200),

ii. in case the power required by the electric supply network 9 increases (step 202),

a) by activating at least one control unit 6 (step 204), increasing the displacement of at least one variable displacement pump/compressor unit 3 (step 206) so as to increase the electric power absorption from the electric supply network 9 by at least one electric motor 5 connected to the electric supply network 9 and actuating said variable displacement pump/compressor unit 3 (step 208),

b) by means of said variable displacement pump/compressor unit 3, accumulating part of the energy absorbed by the electric motor 5 in a pressure accumulator 4 (step 210); iii. in case the power required by the electric supply network 9 decreases (step 201),

c) by activating at least one control unit 6 (step 203), reducing the displacement of at least one variable displacement pump/compressor unit 3 (step 205), d) operating the variable displacement pump/compressor unit 3 as a motor by using the energy previously accumulated by the pressure accumulator 4 (step 207) e) using the variable displacement pump/compressor unit 3 in motor mode to operate the electric motor 5 as an electric generator (step 209),

f) releasing the electric energy produced by the electric generator to the electric supply network 9 (step 211).

In particular, the displacement of said variable displacement pump/compressor unit 3 is increased when a power supplied from the electric supply network 9 lower than a predetermined threshold value of maximum average power preferably ranging between 5 kW and 50 MW is detected, even more preferably ranging between 10 kW and 20 MW, and the displacement of said variable displacement pump/compressor unit 3 is reduced when a power supplied from the electric supply network 9 higher than a predetermined threshold value of maximum average power preferably ranging between 5 kW and 50 MW is detected, even more preferably ranging between 10 kW and 20 MW.

In the method described, moreover, the electric power absorbed by or delivered to the electric supply network 9 by said electric appliance 2 connected to the electric supply network 9 or by said plurality of appliances 2A',2A",..., 2Aⁿ connected to the electric supply network 9 is detected, and the displacement of the variable displacement pump/compressor unit 3 is controlled depending on the electric power absorbed or delivered by said electric appliance 2 or by said plurality of appliances 2A',2A", ..., 2Aⁿ.

In particular, with reference to the variant shown in Figure 1A, said at least one sensor S2A or the connection to the control system of the plurality of appliances 2A',2A",...,2Aⁿ can detect the instantaneous power peak resulting from the sum of the powers absorbed or delivered by the plurality of appliances 2A',2A",..., 2Aⁿ and said at least one control unit 6 can adjust one or more branches powering the appliances 2A',2A",..., 2Aⁿ involved in the energy recovery; since the generators power very large networks, not only on shore, but also on board the naval vessels, this recovery is limited to the network branch involved in the power variations that are to be compensated.

More precisely, said at least one sensor S2A or the connection to the control system of the plurality of appliances 2A',2A",...,2Aⁿ is connected to said electric supply network 9 so as to detect the power balance on the electric supply network 9 taking into account the powers absorbed by or delivered to the plurality of appliances 2A'_/2A"_/..._/ 2Aⁿ connected to the electric supply network 9.

With reference to Figure 3, the preferred embodiment of the present invention is described and, precisely, an energy recovery system 10 employed in combination with a heave compensator 20.

As a heave compensator, or vertical motion compensator, is meant an apparatus used in the offshore field - therefore, mainly for the actuation of winches and cranes installed on ships and floating platforms - to stabilize a load during the operations of lifting and positioning the load on the sea floor or on fixed basements; a heave compensator comprises at least one main electric motor 21, actuating at least one lifting system, for example comprising a winch 22 and a pulley 23, and at least one load 24, said load 24 being connected to said electric motor 21 through the said lifting system (winch 22, pulley 23, etc.).

Said main electric motor 21 is suitable to actuate said lifting system 22,23 for lifting and lowering said load 24; said main electric motor 21 is operatively connected to a control system for controlling the descent of the load 24 in the presence of waves and it is connected to an electric supply network 90 to which an electric generator 70 provides the electric supply.

The energy recovery system shown in Figure 3, denoted as a whole by the reference number 10, comprises at least one variable displacement pump/compressor unit 30 fed with a fluid (a gas such as, but not exclusively, air or nitrogen or a liquid such as, but not exclusively, oil or water) optionally contained in a tank 80.

Preferably, said pump/compressor unit 30 is of the variable displacement type with proportional displacement control; preferably, said variable displacement pump/compressor unit 30 has an operating pressure depending on the used fluid, on the required dynamics and on the amount of energy to be stored as well as on the currently available technology (approximately, the pressures can vary from few units to several hundreds bar).

Said variable displacement pump/compressor unit 30 is connected to an accumulator 40, preferably a pressure accumulator; said accumulator 40 can be, for example, of the oleodynamic type, but different fluids such as water, gas and the like could be similarly used.

Preferably, said accumulator 40 is of the bag, piston or membrane type when a liquid is used or a it is a simple pressurized tank if using a gas. Said variable displacement pump/compressor unit 30 is connected through a first duct 340 to said pressure accumulator 40 and in case through an optional second duct 380 to said tank 80.

Said variable displacement pump/compressor unit 30 is further connected to an electric motor 50 that, in turn, is connected to an electric supply network 90 powered by a generation system 70.

Said electric motor 50 is suitable to actuate said variable displacement pump/compressor unit 30 and it is also suitable to be powered through the electric supply network 90.

Said electric motor 50 and said generator 70 are of the type usually used in the industrial, naval, shipbuilding and similar fields.

Said variable displacement pump/compressor unit 30 is further connected to a control unit 60 that, in turn, is connected to the electric supply network 90 too; specifically, said control unit 60 is operatively connected to said variable displacement pump/compressor unit 30 and it is suitable to vary the displacement thereof.

Preferably, said control unit 60 comprises a processor able to detect the load on the electric supply network 90 and to consequently adjust the energy recovery system 10 so that it absorbs or delivers energy to the electric supply network 90.

Finally, a heave compensator 20 is connected to the same electric supply network 90 that powers said electric motor 50 and said control unit 60, and precisely the electric motor 21 of the heave compensator 20 is connected to said electric supply network 90; this heave compensator can operate with power peaks up to 50 MW and more.

Said heave compensator 20 is connected to at least one sensor S20 for detecting an energy variation available on the electric supply network 90 to which said electric motor 50 is connected; similarly to what above indicated, the term "sensor" is herein intended to mean any device that detects and measures an input physical quantity and provides an output signal for the purpose of measurement or control of the system in which it is used.

Said control unit 60 is arranged to increase/reduce the displacement of said variable displacement pump/compressor unit 30, when an excess or a request of energy occurs, respectively, by said heave compensator 20.

In particular, said control unit 60 is arranged to

- increasing the displacement of said variable displacement pump/compressor unit 30 when said sensor S20 detects that the power required to the electric supply network 90 is lower than the set maximum power threshold, so as to absorb more electric power from the electric supply network 90 through the electric motor 50 and to accumulate part of the energy absorbed by the electric motor 50 in the accumulator pressure 40, and

- reducing the displacement of said variable displacement pump/compressor unit 30 until it acts as a motor when said sensor S20 detects a power request from the electric supply network 90 higher than the set maximum power threshold, so that the pressure accumulator 40 delivers energy to the variable displacement pump/compressor unit 30 that thus acts as a motor, while the electric motor 50 acts as an electric generator releasing electric energy to the electric supply network 90.

More precisely, said control unit 60 proportionally adjusts the displacement of the pump/compressor unit 30 so as to maintain as constant as possible the power absorbed from the electric supply network 90 by limiting the oscillations thereof at around the desired average value.

Even more precisely, said control unit 60 is arranged to increase the displacement of said variable displacement pump/compressor unit 30 when said sensor S20 detects an increase of energy available on the electric supply network 90 higher than a predetermined value that we will indicate as "maximum average power" and said control unit 60 is arranged to reduce the displacement of said variable displacement pump/compressor unit 30 when said sensor S20 detects a request of power from the electric supply network 90 higher than the same "maximum average power" value; said "maximum average power" ranges between few kW and tens MW, preferably it ranges between 5 kW and 50 MW and more, even more preferably it ranges between 10 kW and 20 MW.

Said sensor S20 is connected to said electric supply network 90 so that to detect the electric power absorbed from or delivered to the electric supply network 90 by said heave compensator 20 connected to the electric supply network 90.

In short, in the heave compensation plant 20, the energy recovery system 10 is connected to the electric supply network 90 to absorb or deliver electric energy to said electric supply network 90 depending on the electric power absorbed from or delivered to the electric supply network 90 by said main electric motor 21 of said heave compensation plant 20.

It is worthy herein to underline that the system according to the present invention does not provide mechanical, electric and/or hydraulic connections between the heave compensator 20 and the energy recovery system 10 since the only strictly necessary common connection is the electric supply network 90; the system according to the present invention can be defined as an electric energy accumulator temporarily using pressure accumulators in order to ensure powers that the electric generators are not able to achieve.

In other words, in the heave compensation plant 20, the energy recovery system 10 is connected to the heave compensation system 20 only through the electric supply network 90. For clarity's sake, in Figure 3 only the essential functional components of the system 10 and of the heave compensator 20 are shown, while it is understood that other components may be provided, such as valves, pressure gauges and similar components, suitable for controlling and adjusting the system of the invention as well as of the appliance herein specifically connected.

The described system 10 allows to recover electric energy and to make it available for a subsequent use, as it is clarified hereinafter.

The energy recovery system 10 for heave compensator 20 to be used in the off-shore field benefits from the variable displacement unit 30 actuated by the electric motor 50 connected to the electric network of the ship.

When the main motor 21 of the heave compensator acts as a generator, the control unit 60 acts on the pump/compressor unit 30 to increase the displacement thereof, thus requiring more electric power from the electric network of the ship; in this way the electric energy generated by the main motor 21 is absorbed by the pump/compressor unit 30 and transferred to the accumulator 40.

When the main motor 21 of the heave compensator requires energy from the electric network of the ship in order to actuate the winch 22, part of the energy is recovered from the accumulator 40 by reducing the displacement of the pump/compressor unit 30, so as to operate as a generator the electric motor 50 of the energy recovery system 10.

Similarly to what described for the general embodiment of the present invention applied to a generic appliance or to a plurality of generic appliances, the system 10 described with particular reference to a heave compensator allows to recover electric energy and to make it available for a subsequent use according to the method illustrated in general, whose steps are:

i. detecting, by means of at least one sensor S20, the variation of power supplied by an electric supply network 90 (step 200),

ii. in case of the power required by the electric supply network 90 increases (step 202), a) by activating at least one control unit 60 (step 204), increasing the displacement of at least one variable displacement pump/compressor unit 30 (step 206) so as to increase the electric power absorption from the electric supply network 90 by at least one electric motor 50 connected to the electric supply network 90 and actuating said variable displacement pump/compressor unit 30 (step 208),

b) by means of said variable displacement pump/compressor unit 30 accumulating part of the energy absorbed by the electric motor 50 in a pressure accumulator 40 (step 210);

iii. in case the power required by the electric supply network 90 decreases (step 201), c) by activating at least one control unit 60 (step 203), reducing the displacement of at least one variable displacement pump/compressor unit 30 (step 205),

d) operating the variable displacement pump/compressor unit 30 as a motor by using the energy previously accumulated by the pressure accumulator 40 (step 207),

e) using the variable displacement pump/compressor unit 30 in motor mode to operate the electric motor 50 as an electric generator (step 209),

f) releasing the electric energy produced by the electric generator to the electric supply network 90 (step 211).

As it results evident from the foregoing, the invention provides an energy recovery system, and the relevant method, allowing to achieve, compared with the technical solutions of the prior art, the advantages that are hereinafter highlighted.

Compared with previous mechanical and/or hydraulic systems, the energy recovery system of the invention allows to:

- satisfy very high energy requests;

- operate with power peaks up to 50 MW and more;

- achieve significant overall yield of the system;

- limit the thermal losses.

Further distinctive features of technical improvement compared with the known prior art concern the cheapness, the simplicity of construction, the operative precision, the high reliability and accuracy of the energy recovery system, and of the relevant method, according to the present invention.

On the basis of the above description, it is then understood that the energy recovery system, and the relevant method, according to the present invention achieve the objects and accomplishes the advantages mentioned hereinabove. Finally, it is clear that many other variants may be made to the energy recovery system, and to the relevant method, of the invention, without falling outside the novelty principles inherent in the inventive idea, as well as it is clear that, in the practical implementation of the invention, the materials, the shapes and the dimensions of the illustrated details may be of any type, depending on requirements, and may be replaced with technically equivalent others.

Where the construction features and the techniques mentioned in the following claims are followed by signs or reference numbers, these signs or reference numbers have been introduced with the sole purpose of increasing the intelligibility of the claims themselves and, consequently, they do not have any limiting effect on the interpretation of each element identified, by way of mere example, by such signs or reference numbers.

Claims

1. An energy recovery system (1,10) comprising:

at least one variable displacement pump/compressor unit (3,30) connected through a first duct (34,340) to at least one pressure accumulator (4,40),

at least one electric motor (5,50) suitable to actuate said variable displacement pump/compressor unit (3,30) and suitable to be powered by an electric supply network (9,90), and

at least one control unit (6,60) operatively connected to said variable displacement pump/compressor unit (3,30) and suitable to vary the displacement thereof,

characterised in that it comprises at least one sensor (S2,S2A,S20) for detecting the power supplied by the electric supply network (9,90) on which the energy recovery is performed and to which said electric motor (5,50) is connected,

and in that said control unit (6,60) is arranged for

increasing the displacement of said variable displacement pump/compressor unit (3,30) when said sensor (S2,S2A,S20) detects that the power supplied by the electric supply network (9,90) is lower than a predetermined threshold value of maximum average power, so as to absorb more power from the electric supply network (9,90) by means of the electric motor (5,50) and to accumulate part of the energy absorbed by the electric motor (5,50) in the pressure accumulator (4,40),

reducing the displacement of said variable displacement pump/compressor unit (3,30) when said sensor (S2,S2A,S20) detects that the power supplied by the electric supply network (9,90) is higher than a predetermined threshold value of maximum average power, so that the pressure accumulator (4,40) delivers energy to the variable displacement pump/compressor unit (3,30) that thus acts as a motor, while the electric motor (5,50) acts as an electric generator releasing electric energy to the electric supply network (9,90), the transient state from the operative condition as a pump/compressor unit to the operative condition as a motor being continuous with continuous variation of the power absorbed from / delivered to the electric network.

2. A system (1,10) according to claim 1, wherein said at least one control unit (6,60) is arranged for increasing the displacement of said variable displacement pump/compressor unit (3,30) when said sensor (S2,S2A,S20) detects a value of power supplied by the electric supply network (9,90) lower than the predetermined threshold value of maximum average power, said predetermined threshold value ranging from 5 kW and 50 MW.

3. A system (1,10) according to claim 1, wherein said at least one control unit (6,60) is arranged for reducing the displacement of said variable displacement pump/compressor unit (3,30) when said sensor (S2,S2A,S20) detects a value of power supplied by the electric supply network (9,90) higher than the predetermined threshold value of maximum average power, said predetermined threshold value ranging from 5 kW and 50 MW.

4. A system (1,10) according to claim 1, wherein said at least one sensor (S2,S2A,S20) is connected to said electric supply network (9,90) so as to detect the power balance on the electric supply network (9,90) taking into account the powers absorbed from or delivered to at least one electric appliance (2,2A',2A",..., 2Aⁿ,20) connected to the electric supply network (9,90).

5. A heave compensation plant (20) comprising:

- at least one main electric motor (21) suitable to actuate at least one lifting system

(22,23) for lifting and lowering a load (24) and at least one control system operatively connected to said main electric motor (21) for controlling the position of the load (24) in the presence of oscillations of the ship hull,

at least one electric generator (70) suitable to supply power to at least one electric supply network (90) to which said main electric motor (21) is connected,

characterized in that it comprises an energy recovery system (10) according to any claim 1 to 4, said energy recovery system (10) being connected to said electric supply network (90) to absorb or deliver electric energy from / to said electric supply network (90) depending on the electric power instantly absorbed from or delivered to the electric supply network (90) by said main electric motor (21) of said heave compensator (20).

6. A heave compensation plant (20) according to claim 5, wherein the energy recovery system (10) is connected to the heave compensation plant (20) only by means of the electric supply network (90).

7. A method for energy recovery comprising the steps of:

i. detecting, by means of at least one sensor (S2,S2A,S20), the power supplied by an electric supply network (9,90) (step 200),

ii. in case the power required by the electric supply network (9,90) increases (step 202), a) by activating at least one control unit (6,60) (step 204), increasing the displacement of at least one variable displacement pump/compressor unit (3,30) (step 206) so as to increase the electric power absorption from the electric supply network (9,90) by at least one electric motor (5,50) connected to the electric supply network (9,90) and actuating said variable displacement pump/compressor unit (3,30) (step 208),

b) by means of said variable displacement pump/compressor unit (3,30) accumulating part of the energy absorbed by the electric motor (5,50) in a pressure accumulator (4,40) (step 210);

iii. in case the power required by the electric supply network (9,90) decreases (step 201), c) by activating at least one control unit (6,60) (step 203), reducing the displacement of at least one variable displacement pump/compressor unit (3,30) (step 205),

d) operating the variable displacement pump/compressor unit (3,30) as a motor by using the energy previously accumulated by the pressure accumulator (4,40)

(step 207),

e) using the variable displacement pump/compressor unit (3,30) in motor mode to operate the electric motor (5,50) as an electric generator (step 209), f) releasing the electric energy produced by the electric generator to the electric supply network (9.90) (step 211).

8. A method according to claim 7, wherein the displacement of said variable displacement pump/compressor unit (3,30) is increased when a power supplied from the electric supply network (9,90) lower than a predetermined threshold value of maximum average power ranging from 5 kW to 50 MW is detected.

9. A method according to claim 7, wherein the displacement of said variable displacement pump/compressor unit (3,30) is reduced when a power supplied from the electric supply network (9,90) higher than a predetermined threshold value of maximum average power ranging from 5 kW to 50 MW is detected.

10. A method according to claim 7 or 8 or 9, wherein the electric power absorbed by or delivered to the electric supply network (9,90) by at least one electric appliance

(2,2A',2A",..., 2Aⁿ,20) connected to the electric supply network (9,90) is detected and wherein the displacement of the variable displacement pump/compressor unit (3,30) is controlled depending on the electric power absorbed from or delivered to said at least one electric appliance (2,2A',2A",..., 2Aⁿ,20).