WO2006072791A1

WO2006072791A1 - Energy recovery system

Info

Publication number: WO2006072791A1
Application number: PCT/GB2006/000030
Authority: WO
Inventors: David Cox
Original assignee: Peter Brotherhood Limited
Priority date: 2005-01-07
Filing date: 2006-01-06
Publication date: 2006-07-13
Also published as: GB0500253D0

Abstract

An energy recovery system for recovering waste energy from marine engines comprising a first (102) and second turbine (104) each for generating rotational outputs, electricity generation means (106) for the generation of electrical energy from a rotational input and transfer means (108,112) for transferring the rotational output of the turbines to the rotational input of the generation means. The first turbine is provided on a upstream side of the second turbine, and the second turbine is provided on a upstream side of the generation means. The transfer means comprises means (108) for transferring the first rotational output to an input of the second turbine, and means (112) for transferring the second rotational output to the input of the generation means (106) .

Description

Energy Recovery System

The present invention relates to an energy recovery system and in particular an energy recovery system for recovering waste energy from marine engines.

The recovery of waste heat from marine engines to improve efficiency and reduce fuel costs is a well known technology. Such systems became particularly beneficial in the 1970s when high oil prices improved the economic viability of heat recovery systems.

In recent years, falling real fuel prices reduced the economic benefits of waste heat recovery, although fluctuating oil prices still provide a large impetus for improved efficiency. However, the environmental benefits of reducing fuel consumption by increasing efficiency, are now of key importance in helping to meet commitments made by governments under international agreements such as, for example, the Kyoto agreement to reduce emissions of carbon dioxide. Such commitments have led, for example, to strict statutory controls on the levels of emissions from marine engines, and in particular on emissions from a ship's engines while manoeuvring in port.

Early systems made use of steam turbines to turn waste heat from marine engines into electrical power, thus helping to meet the increasing need for on-board electricity without burning additional fuel.

The drive for even greater efficiency, combined with increased efficiency of marine engine turbochargers, led to improved systems having a combination of power and steam turbines. The steam turbines continued to recover energy from waste heat whilst the power turbines were arranged to recover additional energy from the excess of exhaust gases arising from the improvements to the turbochargers.

An example of an existing combined system is shown in figure 1 generally at 10. The system 10 is configured for the recovery of waste heat from a marine diesel engine 12 having a turbocharger 14. The system comprises a pair of power turbines 16, a steam turbine 18, and an ac alternator 20. Ih operation the power turbines 16 generate rotational energy from waste gases from a marine engine 12, as the gases pass through the turbines 16. The rotational energy generated is transferred via a twin inlet, single outlet parallel shaft gearbox 22, to rotate a shaft 24 at a rotational velocity compatible with the ac alternator 20.

The hot waste gases leaving the power turbines 16 are combined with any other waste gases from the turbocharger 14 before being passed through a waste heat recovery boiler 26. The boiler 26 uses the heat in the waste gases to produce steam for the steam turbine 14.

The steam turbine 18 generates rotational energy from the steam produced. The rotational energy is transferred through a reduction gearbox 28 to the shaft 24. The used steam leaving the turbine 18 is then condensed in a condenser 30 before being returned to the boiler 26, for re-use.

The alternator 20 generates electricity from rotation of the shaft 24. The electricity produced is managed by an energy management system 32 for subsequent distribution for the needs of the ship.

In this arrangement, the steam turbine contributes to an improved efficiency of approximately 8%. Correspondingly, the power turbines contribute approximately 2%. However, the arrangement of a power turbine and steam turbine leads to a number of issues. Firstly, the requirement for a relatively complex parallel shaft gearbox 22 adds expense and complexity to the system. Furthermore, the relative complexity of the gearbox 22 combined with the relatively large gearing ratio required to reduce the rotational velocity from that of the power turbine output (typically 25000 r.p.m) to a speed suitable for the alternator 16 (typically 1800 r.p.m) puts excessive strain on the gearbox thus making it prone to failure.

Maintenance is thus required on a more regular basis, than might otherwise be necessary, to ensure the system remains functional. This issue is compounded by the fact that when either power turbine requires maintenance the whole system has to be shut down, despite the other turbine remaining operational. If maintenance is needed, therefore, while continued use of the engine is required, for example whilst a ship is at sea, there is a significant reduction in efficiency, while repairs and/or other maintenance are completed. In some cases, the whole system may have to be shut down until the ship is in port.

Additionally, the system requires a specially designed, dual input generator, for the generation of electricity from the rotation of the shaft 24. This also adds further cost and complexity and decreases the reliability of the system.

The present invention relates to an energy recovery system, which significantly mitigates the above issues.

Acording to the invention there is provided an energy recovery system for recovering waste energy from marine engines comprising: a first turbine for generating a first rotational output; a second turbine for generating a second rotational output; electricity generation means for the generation of electrical energy from a rotational input; and transfer means for transferring the rotational output of said turbines to. the rotational input of said generation means; wherein: said first turbine is provided on a upstream side of said second turbine, and said second turbine is provided on a upstream side of said generation means; said transfer means comprises means for transferring said first rotational output to an input of said second turbine, and means for transferring said second rotational output to said input of said generation means.

Preferably one of said first and second turbines is a power turbine for generating the corresponding rotational output from the flow of gases.

Preferably one of said first and second turbines is a steam turbine for generating the corresponding rotational output from heat.

Preferably said first turbine is a power turbine and said second turbine is a steam turbine.

Preferably said transfer means comprises a gearbox for gearing the rotational output of the first turbine relative to the input of said second turbine. Said gearbox may comprise clutch means for disengaging the rotational output of said first turbine relative to the input of said second turbine. Said clutch means may comprise a freewheeling clutch having engageable input and output portions, configured to automatically engage as the rotational velocity of the input portion approaches that of the output portion, and to disengage as the rotational velocity of the input portion decreases below that of the output portion.

Preferably said transfer means comprises a or a further gearbox for gearing the rotational output of said second turbine relative to the rotation of input of the generation means.

The invention will now be described by way of example only with reference to the attached figures, in which:

Figure 1 is a simplified schematic of a prior art energy recovery system;

Figure 2 is a simplified schematic of an energy recovery system according to the invention;

Figure 3 is a perspective view of a portion of a gearbox for the energy recovery system of figure 2;

Figure 4 is a first cross-sectional view of the gearbox of figure 3;

Figure 5 is a second cross-sectional view of the gearbox of figure 3;

Figure 6 is a cross-sectional illustrative view of a clutch for the gearbox of figure 3; and

Figure 7 is a part section showing a pawl assembly for the clutch of figure 6.

In figure 2, an improved energy efficiency system is shown generally at 100. The system 100 shown is configured for the recovery of waste heat from a marine diesel engine 12, having a turbocharger 14. It will be appreciated, however, that the system 100 maybe used to recover energy from other forms of engine, such as for example static engines in industrial plants.

Like the prior art system 10, the new system 100 comprises a power turbine 102, a steam turbine 104, and a generator 106. However, in the new system 100 both the power turbine 102 and the steam turbine 104 are positioned in general mechanical alignment, on a upstream side of the generator 106, as seen in figure 2.

The power turbine 102 is configured to drive a rotational output from excess waste gases produced by the engine 12. The rotational output is mechanically coupled for the transfer of rotational energy to an input of the steam turbine 104, via a first reduction gearbox 108. In operation, the first gearbox 108 reduces the rotational velocity of the power turbine output (typically 19500 r.p.m) for compatibility with the steam turbine 104 (typically 6800 r.p.m).

The power turbine 102 is of a gas expander type, although it will be appreciated that any suitable power turbine 102 may be used. It will be appreciated, however, that the power turbine may be of any suitable type.

The steam turbine 104 is configured to drive a rotational output from steam produced from water heated by the passage of the excess hot waste gases through a boiler 110. The input of the steam turbine 104 and the corresponding rotational output are mechanically coupled such that, in operation, the rotational output is driven both directly by the steam turbine 104, and indirectly via the first gearbox 108, by the rotational output of the power turbine 102.

The rotational output of the steam turbine 102 is mechanically coupled to a rotational input of the generator 106 via a second reduction gearbox 112. In operation, the second gearbox 112 reduces the rotational velocity of the steam turbine output (typically 6800 r.p.m) for compatibility with the generator 106 (typically 1800 r.p.m).

The steam turbine 104, is of a dual pressure type, and the boiler 110 is of a type having at least two steam outputs 114, suitable for supplying steam to the dual pressure turbine 104. It will be appreciated, however, that the steam turbine and boiler maybe of any suitable type, for example, a single pressure steam turbine, and a single steam output boiler, or the like.

A condenser 116 is provided on a steam output from the steam turbine 104 for re-condensing steam exiting the turbine 104. In operation, the re-condensed steam is passed back to the boiler 110 from the condenser via suitable conduits for subsequent reuse. The recycled water is then re-heated to generate more steam, which is used to drive the steam turbine and hence the process continues.

The boiler 110 is further provided with at least one waste gas output 118 for venting exhaust gasses once the heat has been extracted from them to generate steam.

The generator 106 comprises any suitable electricity generation means, for example, a single input ac alternator. In operation, therefore, the alternator 106 generates electricity from the rotational input, which in turn is driven by the rotational outputs of the power and steam turbines 102, 104, via the first and second gear boxes 108, 112.

The electricity produced by the alternator is managed by an energy management system 32 for subsequent re-distribution for the needs of the ship, in a similar manner to the prior art system of figure 1.

Figures 3 to 5 show a gearbox of a type suitable for use as the first gearbox 108. The gearbox 108 is generally of conventional design and will be described only to the extent necessary for an understanding of the invention. The gearbox 108 comprises axially parallel input and output trains 120, 122. The input trainl20 comprises an axially aligned rotational input 124 and input pinion 126. Correspondingly, the output train 122 includes an output end 128, comprising a rotational output 130; and an input end 132, comprising a driven gear 134, axially aligned with the output 130. The output train 122 is further provided with clutch means 136, intermediate the input and output ends 132, 128 for mechanically coupling and decoupling the output end 128 to and from the input end 132 respectively.

The input pinion 126 and driven gear 134 are arranged transversely adj acent one another for mutual engagement. The gearing ratio between the pinion 126 and the driven gear 134 may be of any suitable ratio, but is typically, for example, approximately a 3:1 ratio. Hence, in operation, rotation of the input 124 produces corresponding rotation of the pinion 126, which in turn drives the driven gear 132.

The clutch 136 is a freewheeling clutch, which is configured to engage and disengage in dependence on differences in speed between the input and output ends 132, 128, of the output train 122. Thus, in operation, when power is applied to the input end 132, and its speed matches or tends to exceed that of the output end 128, the clutch 136 engages. Contrastingly, any sustained negative torques, when the clutch 136 is engaged, causes the clutch 136 to disengage.

When the gearbox 108 is in position in the system 100, the input train 120 is coupled to the rotational output of the power turbine 102 and the output end of the output train 122 is coupled to the rotational input of the steam turbine 104.

In operation, therefore, when the steam turbine 104 is running, generating the corresponding rotational output, there is associated rotation of the turbine rotational input and hence the output end 128 of the output train 122. While the power turbine 102 is at rest, the gearbox rotational input 124, and the input end 128 of the output train 122, are also at rest. Thus, there is a difference in rotational speed between the input and output ends 132, 128, and the clutch 136 is disengaged.

If the power turbine 102 is then started, the corresponding rotational output accelerates towards an operational speed. Thus, the gearbox rotational input 124, and hence input end

128 also begin to accelerate toward respective operational speeds depending on the gearing ratio between them. As the speed of the input end 128 approaches that of the output end 132 the clutch 136 automatically engages and power is transmitted from the power turbine 102 through the gearbox 108, and the steam turbine 104, to the rotational input of the alternator 106.

If the power turbine 102 is subsequently stopped, the corresponding rotational output decelerates towards rest, slowing the input end 128 of the gearbox output train 122, hence disengaging the clutch 136. Thus, the steam turbine 104, can continue to operate.

In figure 6, an embodiment of a clutch suitable for inclusion in the gearbox is shown generally at 150. For ease of understanding the upper and lower portions of figure 6, as defined by the axial line AA', show the clutch 150 in a disengaged position and an engaged position respectively. Despite the differences in appearance between the clutch 150 and the clutch 136 shown in figures 3 to 5, the clutches 136, 150 operate in essentially the same manner and hence the description of them is generally applicable to both embodiments.

The clutch 150, comprises an input portion 152, a sliding portion 154, and an output portion 156.

The input portion 152 comprises an input shaft 158 having a generally cylindrical receiving section 160 for slidably receiving the sliding portion 154. Correspondingly, the sliding portion is generally annular of internal dimensions suitable for slidable reception on the input shaft 158. The receiving section is provided with external helical splines arranged for mutual engagement with corresponding internal helical formations on the sliding portion 154.

The sliding portion 154 is received on the receiving section 160 and in operation is helically slidable between a first disengaged position, D, and a second engaged position, E.

The splines are arranged such that, in operation, when the sliding portion 154 is in the engaged position E, rotation of the sliding section 154 in a rotational direction C relative to the input portion 152, results in the sliding portion 154 moving on the splines towards the disengaged position.

Conversely, in operation, when the sliding portion 154 is in the disengaged position D, rotation of the sliding section 154 in an opposing rotational direction C relative to the input portion 152, results in the sliding portion 154 moving on the splines towards the engaged position.

When the clutch 150 is assembled in position in the gearbox 108, the input shaft 158 is fixed to and coaxially aligned with the input end 132 of the output train 122, generally intermediate the input and output ends 132, 128. The shaft 158 maybe fixed using any suitable means, for example nuts and bolts or the like.

The sliding portion 154 is further provided with external clutch teeth 162 and external ratchet teeth 164. The output portion 156 comprises a generally annular clutch ring 166 having internal clutch teeth 168. The internal teeth 168 and the dimensions of the ring 166 are configured for mutual engagement with the external clutch teeth 162 of the sliding portion 154, when the sliding portion 154 is in the engaged position E.

When the clutch 150 is assembled in position in the gearbox 108, the clutch ring 166 is fixed to the output end 128 of the output train 122. The clutch ring 166 is positioned coaxially with the output train 122, generally intermediate the input and output ends 132, 128, such that when the sliding portion 154 is in the engaged position E, the internal and external clutch teeth 168, 162 are mutually engaged. The ring 166 may be fixed using any suitable means, for example nuts and bolts or the like.

The output portion 156 is further provided with an internal recess 170 for receiving pawl assemblies 180. The recess 170 extends generally radially from an internal surface of the ring 166 and, when the clutch 150 is assembled, is located generally radially adjacent the position the ratchet teeth 164 occupy when thp sliding portion 154 is in the disengaged position D.

Referring now to figure 7, each pawl assembly 180 comprises a pawl 182, a biasing spring 184 and a stop 186. The pawl 182 is mounted on a pivot 187 within the recess 170, for rotation about an axis BB' running generally parallel to the rotational axis AA' of the clutch. The spring 184 is configured to rotationally bias the pawl 182 into a first rotational or engaged position. The stop 186 is located for engagement with a protruding section 188 of the pawl 182 to substantially prevent further rotation of the pawl 182 from the first position in the rotational direction of the spring bias. Figure 7 shows the pawl 182 in the first rotational position.

The pawl 182 also comprises an engagement section 190, which extends outwardly from the recess 170, when the pawl is in the first rotational position, for engagement with at least one of the ratchet teeth 164, when the sliding portion 154 is in the disengaged position D. The pawl 182 is rotatable against the bias of the spring into a further rotational position in which the engagement section 190 is partially, or completely received within the recess 170 such that it is not engaged with the ratchet teeth 164. The pawl 182 is shaped such that when the engagement section 190 is engaged against one of the ratchet teeth 164, rotation of the sliding portion 154, relative to the output ring 156 is substantially prevented, in the direction C. The shape of the pawl 182 is also such that rotation of the sliding portion 154, relative to the output ring 156, in the opposing rotational direction C, simply results in the pawl 182 being rotated against the spring bias thereby to disengage the pawl 182 from the ratchet teeth 164.

When assembled in gearbox 108, the rotational direction C corresponds to the rotational direction of the output train 122, during normal operation. Hence, relative rotation of the sliding portion 154, in the opposing direction C will generally only occur when, in operation, the output portion 156 of the clutch 150 is rotating faster then the input portion 152.

It will be appreciated that the groove may have any appropriate number of assemblies 180, in positions suitable for substantially simultaneous engagement with corresponding ratchet teeth 164, to align the external and internal clutch teeth 162, 168. Typically, however, there are two pawl assemblies 180.

Typical operation, to engage the clutch from rest will now be described by way of example only.

Initially, for example, the input and output portions 152, 156, are stationary and the sliding portion 154 is in the disengaged position D. Drive is then applied to rotate the input portion 152, as the input shaft 158 rotates, each pawl 182 engages with corresponding ratchet teeth 164 for alignment of the external and internal clutch teeth 162, 168.

As the input portion 152 continues to rotate, torque induces the sliding portion 154 to move axially along the helical splines toward the engaged position E. As the sliding portion 154 moves into the engaged position E, the complementary clutch teeth 162, 168 pass smoothly into mesh. Torque is thus transmitted to the output portion 156.

As the clutch teeth 162, 168 move into mesh, the ratchet teeth 164 move out of transverse alignment with the recess 170 and hence the pawl assemblies 180. Hence the pawls are unloaded and thus the torque applied to them is only that required to move the sliding portion 154 into engagement.

Conveniently, the final part of the engagement process is cushioned by the actuation of an oil- fed dashpot formed by the annular space between the sliding portion 154 and the. receiving section 160 of the input portion 152.

Typical operation, to disengage the clutch 150 at speed will now be described by way of example only.

Initially, for example, the input and output portions 152, 156, are rotating at substantially the same speed and the sliding portion 154 is in the engaged position E. When the speed of output portion 156 accelerates beyond that of the input portion 152 (or the input portion 152 slows), torque reversal occurs and the sliding portion 154 is forced to move axially along the helical splines toward the disengaged position D.

As the output portion 156 accelerates, centrifugal force acts the pawl assemblies 180 to retract the pawls 180 into the recess 170 against the spring bias, thus preventing undesirable ratcheting occurring while the clutch is overrunning.

Thus, drive to the input portion 152 can be stopped at any time without affecting the operation of machinery, such as a steam turbine, coupled to the output.

Typical operation, to re-engage the clutch 150 at speed will now be described by way of example only.

Initially, for example, the input portion 152 is at rest, the output portion 156 is rotating at speed, and the sliding portion 154 is in the disengaged position D. Drive to the input portion 152 is reapplied to begin accelerating the speed of the input 152 toward that of output portion 154.

When the speed of the input portion 154 matches that of the rotating output portion 156, the pawls engage in the ratchet teeth 164 and hence the sliding portion is moved into the position as described previously.

Once the clutch is re-engaged, drive to the input portion 152 is transferred to the output portion 156 and hence any machinery coupled to it.

Typical operation, of the system 100 will now be described by way of example only.

In operation gases 200 produced by the engine 12 are used by the turbocharger 14. Excess gasses 202, not used by turbocharger 14, are directed to the power turbine 102,

The power turbine 102 utilises the excess gasses 202 to drive the corresponding rotational output, and hence the rotational input of the generator 106 via the steam turbine 104 and the gearboxes 108, 112.

Hot gasses 204 exiting the power turbine 102 are combined with hot turbocharger gasses 206 and are subsequently directed to the boiler 110. Heat from gasses 204, 206, is transferred to water to generate steam. Steam flow 208 from the boiler 110 is directed to the steam turbine 104. Once heat from gasses 204, 206 has been removed the gasses are vented.

The steam turbine 104 generates rotational energy from the steam, for driving the corresponding rotational output, and hence the rotational input of the generator 106 via the gearbox 112. Steam flow 210 from the turbine 104 is directed to condenser 116 where it is condensed back to water before flowing back to the boiler 110 for subsequent reuse.

The generator 106 generates electricity from the rotational energy applied to the associated rotational input. Electricity flow 212 ^'from the generator 106 is directed to the energy management system for distribution for the needs of the ship.

Claims

1 An energy recovery system for recovering waste energy from marine engines comprising:

a first turbine for generating a first rotational output;

a second turbine for generating a second rotational output;

electricity generation means for the generation of electrical energy from a rotational input;

and transfer means for transferring the rotational output of said turbines to the rotational input of said generation means;

wherein:

said first turbine is provided on a upstream side of said second turbine, and said second turbine is provided on a upstream side of said generation means;

said transfer means comprises means for transferring said first rotational output to an input of said second turbine, and means for transferring said second rotational output to said input of said generation means.

A heat recovery system as claimed in claim 1 wherein one of said first and second turbines is a power turbine for generating the corresponding rotational output from the flow of gases.

A heat recovery system as claimed in claim 1 or 2 wherein one of said first and second turbines is a steam turbine for generating the corresponding rotational output from heat.

A heat recovery system as claimed in claim 1 wherein said first turbine is a power turbine and said second turbine is a steam turbine. A heat recovery system as claimed in any preceding claim wherein said transfer means comprises a gearbox for gearing the rotational output of the first turbine relative to the input of said second turbine.

A heat recovery system as claimed in claim 5 wherein said gearbox comprises clutch means for disengaging the rotational output of said first turbine relative to the input of said second turbine.

A heat recovery system as claimed in claim 6 wherein said clutch means comprise a freewheeling clutch having engageable input and output portions, configured to automatically engage as the rotational velocity of the input portion approaches that of the output portion, and to disengage as the rotational velocity of the input portion decreases below that of the output portion.

A heat recovery system as claimed in any preceding claim wherein said transfer means comprises a or a further gearbox for gearing the rotational output of said second turbine relative to the rotation of input of the generation means.