WO1999022120A1

WO1999022120A1 - Energy recovery and conversion system for mobile devices

Info

Publication number: WO1999022120A1
Application number: PCT/SE1998/001958
Authority: WO
Inventors: Matt Miskimin; Wolfgang Feldman; Stephan Sicars
Original assignee: CARRICKFERGUS AB
Current assignee: CARRICKFERGUS AB
Priority date: 1997-10-28
Filing date: 1998-10-28
Publication date: 1999-05-06
Anticipated expiration: 2000-04-28
Also published as: AU9773398A; SE9703947D0

Abstract

An energy conversion system for a motor vehicle, locomotive, rail car, tram or water vessel, wherein low temperature waste heat from one or more encapsulated exothermic devices are used to power a thermodynamic cycle means (500) which generates mechanical energy.

Description

TITLE: Energy recovery and conversion system for mobile devices

TECHNICAL FIELD:

The present invention relates to a thermal energy recovery and conversion system capable of functioning at temperatures of 95° C and higher in mobile applications

(i.e. motor vehicles, ships and rail bound equipment) particularly for providing energy for use in drive and auxiliary systems like lighting air conditioning and refrigeration systems according to the preamble of claim 1.

For the purposes of this document, the term "vehicle" will be used to represent busses, trucks, rail-bound vehicles and marine vessels.

BACKGROUND OF THE INVENTION:

The demands placed on the public transport system and related vehicles are becoming increasingly complex. These demands include refrigeration or air conditioning functions for the passengers, improved fuel efficiency of the vehicle and reduced operator's costs in terms of both purchase costs and running costs. In addition, increasing awareness of global environmental issues and government legislation is forcing manufactures to use more environmentally friendly materials in the construction and operation of vehicles .

The list of new demands includes reduction of the levels of noxious gas and solid particle pollutants emitted by the vehicle, maximum possible vehicle efficiency and increased availability of heating and cooling or refrigeration capacity to provide the desired temperatures in the cabin and cargo areas. Further, demands for recyclability of components and a general reduction of the use of environmentally damaging practices and products are increasing.

Advances in internal combustion motor technology have, through a combination of new technologies, increased the fuel efficiency and reduced the heat energy output of diesel engines, the most common heavy vehicle power-plant today. The most marked change in the characteristics of the newer engines is that they generally operate with much lower heat losses compared to older engines. The available energy for use in the vehicle via traditional water-based heating circuits has been effectively halved. At the same time, the recent advances made in electric drive technology and thyristor-based controls have opened the door for new thinking in the area of efficiency and environmental impact .

The most common forms of propulsion units in heavy road vehicles are still diesel engines, coupled to mechanical gearboxes and drive shafts. These propulsion units have, over the past decade, increased in efficiency and reliability, although some negative attributes still remain. Less than 35 to 40 % of the total energy released from the fuel consumed during a normal drive cycle is effectively utilized as work energy, while the remaining 60 to 65 % is released in the form of heat through the cooling process or as exhaust/waste heat. The energy required to perform braking functions on the heavy vehicles is usually provided by hydraulic/pneumatic systems powered by the diesel engine. The braking activity changes kinetic energy into thermal energy. Material abrasion of brake disks and brake pads, or the equivalent brake parts, cause this conversion of energy.

Common propulsion units in trains are diesel-electric, diesel-hydraulic or electric. The hydraulic drive of such a system commonly have an efficiency of roughly 85 % (nominal value). This applies to systems based on diesel motors. In electric based systems, the transformer unit commonly has an optimal (nominal value) efficiency of 92 to 94 %. The drive motors and inverters have similar values.

An increasingly widespread use of air conditioning and refrigeration systems in busses, ships, trains and trucks is brought by the demands of the modern transport industry. The cooling units employed usually comprise standard format machines with compressors, evaporators and radiator packs based on R-134a type coolants. In some cases, C0₂ or other natural refrigerants are used to reduce the environmental and safety risks in handling and maintenance procedures. The normal effective cooling capacities of these systems varies commercially but can easily be in the range of 30 to 60 kW for land-based vehicles and up to several MW for marine vessels. The cargo or cabin heat exchanger is also dependent upon energy supplied by the engine cooling circuit. The output power of the cooling compressor, condenser and heat exchanger also varies but are dependent upon the power of the compressor which commonly is driven by belts connected to the vehicle's engine's flywheel. This extra workload reduces the available power to the drive train and therefore increases vehicle fuel consumption. These climate control units may also be designed to introduce fresh air into the cabin or use re-circulated air from the cabin under certain conditions. Those conditions include initial vehicle cool-down periods and periods when the external air contains unacceptable amounts of pollution in either gaseous or particulate form. This function is usually accomplished through the opening and closing of air intake flaps.

Standard practice today in performing air conditioning or refrigeration operations in vehicles utilizes separate devices for cooling and heating the cabin and the cargo space. Often, there is a smaller climate control system for the cabin using a standard compressor of the type used in automobile applications, run directly off the engine. In addition, there may be a larger refrigeration unit mounted on the chassis or the truck body for maintaining the desired cargo temperature. Typically, such refrigeration units are powered by a smaller diesel engine, which consumes fuel and adds weight to the vehicle. Both systems thus increase the workload of the propulsion engine in order to perform their functions. Neither device in current form fulfils the functional demands placed on the other device, which results in two or more systems or devices being necessary to perform one group function in the vehicle, i.e. climate control and temperature regulation.

The level of air filtration in the vehicle is often minimal. In most cases, a simple filter element is installed at the air intake of the air conditioning unit and sometimes a second filter element is found at the air inlet to the cabin. In general, these filter elements are changed on a calendar scheme and lack the ability to indicate their flow-through capacities or status.

In times of winter operation with the engine coolant based heating circuit in use, or in vehicles which lack air conditioning units altogether and use defroster packs alone, there may be used a simple filter element at the air inlet to the cabin. In most cases, the filter function is rudimentary and designed to remove dust or other larger particles from the air.

The optimization of humidity levels in the cabin and cargo areas is possible when an air conditioning unit is in place and in use. The removal of any excess humidity from these areas caused by introduction of new non-uniform temperature materials, foodstuffs etc. is a primary function for these units .

As described, for example, in US-A-4 888 959, the compressor is commonly driven by the vehicle's engine, something which reduces power to the drive train and increases fuel consumption.

In order to, at least partially, overcome some of the drawbacks associated with compressor-driven air- conditioning units, so-called refrigerating absorption systems have been developed which utilize the exhaust gas of the vehicle engine as a source of heat. In this respect, EP-A-O 350 764 and DE-C-41 42 314 can be mentioned by way of example.

The above-mentioned solutions to vehicle propulsion and air conditioning are associated with several drawbacks. For example, there may be mentioned higher loads on the propulsion unit resulting in higher fuel consumption and relatively complex systems having a plurality of components prone to breakage resulting in high maintenance costs.

To chill air, a "state of the art" process called the "Compression-Cold Steam" process is known where a compressor is used to compress a coolant medium. The coolant is lead to a condenser where it is cooled and heat is thus conveyed to the air outside the area, which is to be chilled. Next, the coolant is expanded, via an expansion valve, in an evaporator where it is heated by the air to be chilled, thus cooling the air.

This process requires power to drive the compressor and one suitable power source is a machine working according to the Rankine Cycle. The Rankine Cycle machine will be described in detail later.

SUMMARY OF THE INVENTION: It is therefore an object of the present invention to provide a _.mechanical and/or electric energy generating system, which minimizes the drawbacks and thermal energy inefficiencies associated with transport systems having drive trains combining combustion engines and/or turbines, gears, hydraulic drives, electrical equipment such as motors, transformers and/or inverters, and braking systems.

This object is achieved by the energy conversion system as claimed in claim 1.

Preferred embodiments of the invention are detailed in the respective dependent claims.

The present invention thus provides a thermal conversion system in which a per se known technique, the Rankine Cycle process, is utilized in a new context together with numerous different methods for increasing the thermal efficiency of this technique when applied to "vehicles".

BRIEF DESCRIPTION OF THE DRAWINGS:

The invention will be described in the following in greater detail by way of example only and with reference to the embodiments shown in the drawings. Fig. 1 is a schematic representation of a state of the art energy conversion system according to the Rankine cycle,

Fig. 2 is a schematic representation of a Rankine Cycle coupled to a waste heat removal/capture system and an energy storage device with electrical energy generating capacity

Fig. 3 is a schematic representation of an embodiment of an energy conversion system according to the present invention,

Fig. 4 is a schematic representation of another embodiment of an energy conversion system according to the present invention,

Fig. 5 is a schematic representation of a further embodiment of an energy conversion system according to the present invention,

Fig. 6 is a schematic representation of yet another embodiment of an energy conversion system according to the present invention,

Fig. 7 is a schematic representation of yet another embodiment of an energy conversion system according to the present invention,

Fig. 8 is a schematic representation of yet another embodiment of an energy conversion system according to the present invention, and

Fig. 9 is a schematic representation of yet another embodiment of an energy conversion system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS: A number of ways are known to individually cool heat sources in a motor vehicle, locomotive, rail car, tram or marine vessel. Examples are cooling by radiation, by airflow (with or without an additional blower) or by a cooling fluid which passes a heat exchanger. On marine vessels, a second circuit that is cooled in a second heat exchanger by the ambient water is often utilized. According to the invention, the cooling system is integrated with the Rankine cycle which is used as part of the heat sink.

It is also known that the temperature level during operation of any mentioned propulsion device (hereafter referred to as exothermic devices) is to be kept within a certain range, and that radiation to the ambient air is used as heat transfer. In a preferred embodiment the uncontrolled energy flow by radiation is avoided through thermal encapsulation of the devices and by channeling the waste heat into the Rankine cycle. It is possible that the temperature of the exothermic devices will exceed the operating temperature of the cooling or lubrication fluids.

In such cases synthetic oils may be used or the pressure of the cooling medium will be raised to prevent boiling or phase change .

Since a reduced amount of energy in the form of lost or waste heat from different sources is available, the introduction of insulation or encapsulation of heat emitting units can in most cases, optimize the waste heat conversion process. This will increase the efficiency of the entire system and collect the waste heat (energy resource) and channel it back into a useful thermodynamic process. Radiated heat energy is thus minimized and efficiency is optimized.

Hence, increasing the temperature (in case of one-phase fluids without phase change) or pressure and temperature (in cases of fluids with phase change or two-phase fluids) of the cooling medium of the heat sources (the drive motors, transformers, gearboxes etc.) is advantageous for the system.

In another embodiment the overall efficiency of the system is raised, such that a maximum amount of recaptured energy is delivered to the Rankine cycle by using a cascade system. In this system, all of the exothermal devices are arranged in series (or parallel if need be) so that the cooling medium leaving the Rankine cycle heat exchanger cools the exothermic device having the lowest operating temperature first. The medium then moves through the system finally coming to the exothermal device having the highest operating temperature. From this point the cooling medium is returned to the Rankine cycle with the greatest amount of absorbed energy.

In another preferred embodiment a heat storage device is provided. This can be of use if a train or other vehicle passes through a very long tunnel, which may have limited aspiration means due to high costs or physiological obstacles. In this case, the cooling system of the train can store the heat for a certain time due to the masses of the cooling medium and the volume of the Rankine cycle work-fluid storage device. This could dramatically reduce overall tunnel costs, both for construction and maintenance.

In another preferred embodiment the operating temperature of electrically driven trains is regulated. This can be done by taking advantage of the normal condition for electric trains that normally have relatively high installed power confined to a relatively small space, which normally results in high levels of lost waste heat energy. In this case, the operating temperature could be raised to a point where waste heat recovery can be realized economically.

In Fig. 1, a known Rankine cycle device 500 is shown. It comprises an evaporator 540, an expansion machine 510, a condenser 520 and a working fluid pump 530. The evaporator 540 conveys heat to the work fluid, this heat energy being represented by the arrow B. Mechanical energy is obtained in the expansion machine 510 by expanding the work fluid from high to low pressure. The work fluid is condensed at a low temperature in the condenser 520. The pump 530 imparts the necessary evaporation pressure to the work fluid. The mechanical energy obtained from the expansion machine 510 can be used to spin any other machine or be fed into any other drive train to increase the power of such a drive train. For the purposes of this document, the expression "motor" or "generator" will be used to represent any use of the energy taken from the output shaft of the expansion machine 510. The output can, of course, be used to spin an electric motor/generator to produce electric energy. The working fluid pump 530 is driven either by external energy, such as electricity from the utility net, or directly by the expansion machine 510. The arrow A represents the heat given off, from the working fluid to the ambient air, in the condenser 520.

When working at a high load and the energy supply of the

Rankine cycle machine is insufficient the motor/generator can be furnished with external electric energy. When the load is lower, energy can be generated by the motor/generator and used for other purposes, for example to power the working fluid pump or other on board systems, e.g. lighting.

In Fig. 2, a system according to the invention is shown utilizing the energy output by the expansion machine 510 to generate and store electric energy. An energy storing flywheel 400 is connected to the output shaft of the expansion machine 510. The flywheel 400 is connected to a first AC-generator 410, which is connected to a first inverter 420, an energy storage device 430 and a second inverter 440. The first AC-generator 400 supplies electric energy to auxiliary drives 450. The energy storage device 430 may be a battery, fuel cell or similar device. A pump motor 600 supplies the necessary energy to the working fluid pump 530. The energy for the pump motor may be external energy or energy from the expansion machine 510. The waste heat energy fed to the evaporator may come from diesel engines, hydraulic transmissions, mechanical gearboxes, transformers, electric motors, electric generators or inverters, to name a few examples.

Fig. 3 shows a preferred embodiment of the invention, similar to the system shown in Fig. 2. In this embodiment, the expansion machine 510 drives a gearbox 460 with a mechanical energy output. The mechanical energy output is connected to the drive train of the vehicle or vessel, for example via a hydraulic transmission 470.

In Fig. 4, a diesel-mechanical drive is shown as an embodiment for use in trains, busses or trucks, for example. The waste heat coming from the electric equipment of the drive train is conveyed from a first heat exchanger 200 to a working fluid storage 210 and thereafter to the evaporator 540. In addition, waste heat from the diesel- engine coolant and exhaust is also added to the working fluid storage 210 via a second heat exchanger 220. Further waste heat is advantageously added from the transmission gearbox and drive axle gears via a third heat exchanger 230. The electric energy obtained from the expansion machine (as described in Fig. 2) may be used to power an air-condition unit 300. Electric energy is fed to an air- condition motor 310, which drives an air-condition compressor 330, optionally via an energy storing air- condition flywheel 320. An air-condition heat exchanger 340 is driven by an air-condition fan unit 350, which is powered by the electric energy generated by the expansion machine 510.

In Fig. 5, a diesel-hydraulic drive is shown as an embodiment for use in trains, busses or trucks, for example. The system is similar to that of Fig. 4, but waste heat energy from the hydraulic transmission is recuperated via a hydraulic transmission heat exchanger 250. A part of the mechanical energy output of the expansion machine 510 is utilized to put energy into the drive-train via the gearbox 460 with a mechanical energy output, as shown in Fig. 3. The mechanical energy output is connected to the drive train of the vehicle or vessel, for example via a hydraulic transmission 470.

In Fig. 6, a diesel-electric drive is shown as an embodiment for use in trains, busses or trucks, for example. The system is similar to the system shown in Figs. 4 and 5, in that it utilizes waste heat coming from the electric equipment of the drive train, the diesel-engine coolant and exhaust. Further waste heat is advantageously added as waste heat from the electric drive motors 100, via a fourth heat exchanger 110. Advantageously, waste heat energy from a fifth heat exchanger 120 is added from a brake resistor 130 and a brake chopper 140 of the brake system (not shown) . The diesel engine (not shown) drives a second AC-generator 410', optionally via a second energy storing flywheel 400' . The electric energy generated by the second AC-generator 410' is used to drive auxiliary drives. If the amount recovered exceeds the amount that can be consumed by the auxiliary drives, the energy may also be fed into the electric drive motors 100 and the brake system, via a third inverter 420', a second storage device 430' and a fourth inverter 440' .

In Fig. 7, an electric AC drive is shown as an embodiment for use primarily in railbound vehicles. The heat sources are similar to those in Fig. 6, but no diesel engine is present. Instead the waste heat from a transformer 700 is taken via a transformer heat exchanger 710. The transformer 700 feeds electric energy to the drive motors 100 directly via the third inverter 420' and the fourth inverter 440' . The electric energy generated by the second AC-generator 410' is used to drive auxiliary drives and if the amount recovered exceeds the amount that can be consumed by the auxiliary drives, it can also be fed into the drive energy circuit.

In Fig. 8, a diesel-electric drive system for marine vessels is shown. It is similar to the system shown in Fig. 6, but since no brake system is present, no waste heat can be generated by this system. Instead, waste heat is taken from a sixth heat exchanger 150, which recuperates heat energy from the second AC-generator 410' .

In Fig. 9, a diesel-electric drive system for marine vessels is shown. It is similar to the system shown in Fig. 8, but no electric drive motors are used. Instead, waste heat is taken from the sixth heat exchanger 150, which recuperates heat energy from the second AC-generator 410' , as described in Fig. 8.

The invention thus encompasses an energy conversion system for a motor vehicle, locomotive, rail car, tram or vessel, being able to use low temperature waste heat drawn from one or a series of encapsulated exothermic devices i.e. an internal combustion engine or turbine or electric drive, related drive train components like hydraulic transmissions and electrical equipment (especially generators, transformers, electronics (especially those using IGBT) , motors) , gearboxes and brake systems are used to power a thermodynamic cycle which generates mechanical energy (for example the Rankine Cycle having an evaporator, an expansion machine, a condenser and a pump) . The encapsulation is preferably performed using a thermal and/or sound insulating material, and arranged in such a way that maintenance access is not unduly hindered.

To raise the efficiency of the system, the temperature of the cooling medium used to cool the existing heat sources is increased by control of cooling fluid mass flow or similar measures.

The system may advantageously be used as a heat buffer or as an energy storage system under certain conditions the heat flux to the ambient environment is controlled. Said heat sources being cooled by a medium, preferably a fluid, flowing through heat exchangers, which are connected to or cooled by a closed Rankine cycle working fluid cooling circuit.

Additional energy for driving the vapor compression cycle can be supplied by means of an electrical motor, if the system can deliver only limited mechanical energy due to certain waste heat/ambient conditions, or surplus energy recovered by the system can be used for generating electrical energy by the same electrical machine used as a motor now being used as a generator.

The condenser of the Rankine cycle can also be used as the condenser of the vapor compression cycle of machinery used to provide air conditioning and refrigeration to any passenger or freight compartments requiring such. Both functions rejecting the heat to the ambient environment but offering only limited performance in cases of high ambient temperature but high performance during medium and low ambient temperatures .

Mechanical energy generated by the Rankine cycle may be reintroduced to the mechanical systems on board the vehicle .

The encapsulation of the heat generating devices in the system furthermore provides a method for reducing the noise level of the entire transportation device.

Depending upon the extent of application of the energy conversion system according to the invention, the production costs of the vehicle could be reduced by the removal of, for example, auxiliary diesel-powered compressors for cargo refrigeration units, hydraulic drives for fan motors serving engine cooling radiators and clutch and mechanical drive-train. The yearly service costs for the removed equipment is also saved, of course.

There are also large commercial and environmental benefits connected to a system according to the invention such as: reduced electricity or fuel consumption due to the possibility of generating excess electrical power on-board the vehicle, as described previously plus the use of smaller, high efficiency diesel engines via the implementation of a diesel-electric drive setup where electricity to drive and brake the vehicle would be derived from this diesel engine; zero emission operations could be possible when operating on stored electrical energy alone; regeneration of braking energy is easily implemented, using certain types of electric motors for propulsion makes it possible to brake the vehicle under normal operation without using brakes, hence the release of brake dust or pad material is lowered, the same is true regarding the mechanical clutch; reduced noise levels since the diesel engine and drive-train could in certain cases be encapsulated and/or more frequently operated at constant speeds through the drive cycle; reduction of the fuel consumption since the energy used to drive an air conditioning or refrigeration machine could be taken by the Rankine Cycle unit from the engine coolant and the waste heat from the engine exhaust whilst catalyzing the environmentally damaging elements in the gases; better fuel economy will be the result since the power demand on the engine is lowered by the amounts normally associated with direct or hydraulically driven motor cooling fans (approx. 15 kW) and traditional air conditioning compressor technology (approx. 7 kW) . 7Λny decrease in fuel consumption will, naturally, lower the environmental impact over the lifetime of the vehicle.

Naturally, the present invention is not restricted to the embodiments described above and shown in the drawings, but may be varied within the scope of the appended claims.

Claims

CLAIMS :

1. An energy conversion system for a motor vehicle, locomotive, rail car, tram or water vessel, wherein low temperature waste heat from one or more encapsulated exothermic devices are used to power a thermodynamic cycle means (500) which generates mechanical energy.

2. The energy conversion system as claimed in claim 1, wherein the one or more encapsulated exothermic devices are thermally encapsulated.

3. The energy conversion system as claimed in claims 1 or

2, wherein the one or more encapsulated exothermic devices are encapsulated to reduce noise emitted from the devices.

4. The energy conversion system as claimed in claims 1 to

3, wherein the one or more encapsulated exothermic devices comprise an internal combustion engine, a turbine or an electric drive including transformers.

5. The energy conversion system as claimed in claims 1 to

4, wherein the one or more encapsulated exothermic devices further comprise related drive train components (100, 470) and brake system components (130, 140) .

6. The energy conversion system as claimed in claims 1 to

5, wherein the encapsulated exothermic devices are cooled by a medium flowing through one or more heat exchangers (110, 120, 150, 220, 230, 240, 250, 710) which are connected to a closed thermodynamic cycle means (500) working fluid cooling circuit.

7. The energy conversion system as claimed in claims 1 to

6, wherein the temperature of the cooling medium used to cool the encapsulated exothermic devices is increased by control of cooling fluid mass flow to raise the efficiency of the system.

8. The energy conversion system as claimed in claims 1 to

7, wherein the thermodynamic cycle means (500) is a Rankine cycle unit.

9. The energy conversion system as claimed in claims 1 to

8, wherein the Rankine cycle unit comprises an evaporator (540), an expansion machine (510), a condenser (520) and a pump (530) .

10. The energy conversion system as claimed in claims 1 to

9, wherein the system further comprises an electric motor (600) for either adding energy for driving the vapor compression cycle, if the system can deliver only limited mechanical energy due to certain waste heat/ambient conditions, or surplus energy recovered by the system can be used for generating electrical energy by using the electric motor (600) as a generator.

11. The energy conversion system as claimed in claims 1 to

10, wherein one or more exothermic devices used as heat sources are non-encapsulated.

12. The use of an energy conversion system as claimed in claims 1 to 11, as a heat buffer or as an energy storage wherein the heat flux to the ambient environment is controlled.

13. The use of the energy conversion system as claimed in claim 12, wherein the condenser (520) of the thermodynamic cycle means (500) is also used as the condenser of the vapor compression cycle of an air conditioning device (300) and/or a refrigeration device.

14. The use of the energy conversion system as claimed in claims 12 or 13, wherein the mechanical energy generated by the thermodynamic cycle means is reintroduced to the drive train.