Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
  • F01K13/00—General layout or general methods of operation of complete plants
  • F01K13/02—Controlling, e.g. stopping or starting

Definitions

• This invention relates to a device and a method for the operational and safety control of a heat engine. More particularly, it relates to a device for the operational and safety control of a heat engine, which has a working-fluid path including a high-pressure path and a low-pressure path, the heat engine using a condensable working fluid, which is in the liquid phase at least in part of the high-pressure path.
• the invention also relates to a method for the operational and safety control of a heat engine.
• Heat engines exist in many different designs, and are based on different basic principles. More generally, heat engines are also referred to as motors. They share the characteristic of converting thermal energy into a form of higher-grade energy, for example mechanical or electric energy, which has a wider range of application. The majority of heat engines are based on internal combustion, and then at high temperatures (for example > 600 °C). Recently, it has become more and more relevant to use heat at low temperatures to drive heat engines.
• thermal energy available precisely at lower temperatures, and this energy often goes to waste or will have to be removed actively from different systems, for example from industrial processes or from the cooling systems of internal-combustion engines. Utilizing this energy to produce electricity, for example, may be very beneficial as it, as mentioned, often exists as a mere waste-heat product and therefore may be counted as free of cost.
• thermal-energy sources that may potentially be utilized in the same way, for example from gas, oil and biomass combustion, thermal solar collectors, geothermal sources and garbage incineration. Several of these heat sources may have relatively low temperatures, even under normal conditions. In this connection, several technologies based on, inter alia, Stirling and Rankine cycles have been developed, enabling their utilization to produce high-grade energy, generally in the form of electricity.
• ORCs For particularly low temperatures (for example ⁇ 350 °C), motors based on so-called ORCs, the term ORC standing for "Organic Rankine Cycle", are generally used today. Rankine cycles are based on steam-engine processes, in which water is the working fluid, whereas ORCs are based on alternative working fluids, typically with lower boiling points than water, wherein the consequence is a more efficient utilization of the thermal energy. More often than not, these technologies are implemented in closed circuits, in which the working fluid remains in an internal and closed working-fluid circuit including, in the main, two or more heat exchangers, a fluid pump for working fluid and an expander, which may often be a turbine or a piston engine.
• At least one heater section is required, typically in the form of a preheater, a boiler and a superheater, and a cooling section, generally consisting of a condenser, but further components may also be present.
• a heater section may suffice, which is and was also the case in most steam locomotives, as the water (the working fluid) is then usually evacuated into and thereby indirectly cooled in the atmosphere (steam exhaust) after having carried out work by having expanded in the working cylinders.
• the fluid path consists, in the main, of the high-pressure path, which includes all the components from the fluid pump to an expander inclusive, and the low-pressure path, which includes all the components from the expander to the fluid pump inclusive, considering the normal direction of flow of the working fluid.
• the high-pressure path runs from the fluid pump via an outlet in the form of a pressure port, check valves, if any, at the outlet of the pump, connected pipes, further through the heater section which typically consists of the boiler and a superheater, and then to the expander through an inflow/injection valve.
• the low-pressure path then typically runs from the expander, through an exhaust valve and exhaust passage(s), connected pipes and further through the cooler, which at least includes a condenser, a working-fluid reservoir, and then back to the pump through an inlet in the form of a suction port.
• the interfaces separating the high-pressure path from the low-pressure path will then be exactly the fluid pump and the expander.
• the safety valve(s) is (are) arranged to reduce the pressure and possibly the temperature of the working fluid in states of fault/emergency.
• the heated and evaporated working fluid can then be evacuated directly to the cooler, possibly to the working-fluid reservoir, without first having to flow through the expander, so that the temperature and pressure may be reduced as it is cooled by the colder surroundings here. If the cooler should be out of function, such a measure will not be sufficient in the long run. In that case, it must then be possible for the working fluid to be evacuated to an alternative destination, for example into the atmosphere or another open reservoir. With fluids other than water, this could not be a satisfactory solution, either, as several alternative fluids exhibit properties, which make them unfit for discharge into the local environment, either for the reason of human safety, environmental reasons or other reasons.
• the invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.
• the object is achieved through features, which are specified in the description below and in the claims that follow.
• An alternative to letting the heated and evaporated portion of the working fluid be returned to the cooler or an open reservoir is to ensure that, in terms of fluid flow, the working fluid can be drained and evacuated in front of the boiler section, so that the working fluid may then be evacuated from a point in the high-pressure path at which it has not yet undergone evaporation and therefore, in the main, is in the liquid phase.
• the working fluid will be heated successively as it flows through the heater section. That is to say, the portion of working fluid that has flowed the farthest into a heater will normally have received the most heat and thereby reached the highest temperature to the point at which boiling starts, and then normally at a constant temperature.
• the draining point in a portion early enough in the high-pressure path, for example just in front of the heater, or possibly in front of a recuperator, if such a one has been placed in the system, the flow of working fluid could be reversed in a possible need for evacuation.
• the coldest portions of the working fluid present in the high-pressure path will be evacuated first.
• the working fluid that is evacuated will thereby have a minimum of energy, which gives a great advantage if it is going to be evacuated back into the working-fluid reservoir, possibly via the recuperator or cooler (condenser). This will help to limit the final pressure, and also the temperature, reached in the low-pressure path after the evacuation has been completed.
• a drain loop like the one described above could be a very use- ful tool for stopping the operation of the motor in a quick and efficient way.
• the high-pressure path must be drained of working fluid when the operation is to be stopped, and this requires in many cases that the evaporation of the fluid must be continued, while at the same time the working-fluid pump is stopped, in order then to evacuate the working fluid through the expander, possibly through a bypass, but wherein the working fluid will still be in the evaporated state as it is flowing out of the high-pressure path.
• a heat engine which has a working-fluid path including a high-pressure path and a low-pressure path is provided, the heat engine using a condensable working fluid which is in the liquid phase at least in part of the high-pressure path, and the heat engine being characterized by a fluid-drainage path, which is selectably open or closed, being connected to a portion of the high- pressure path in which the working fluid is mainly in the liquid phase.
• the fluid-drainage path may be connected to the high-pressure path at a connection point located downstream of the fluid pump.
• the fluid-drainage path may be connected to the low- pressure path.
• the fluid-drainage path may be provided with a drain valve, preferably in the form of a controllable valve.
• the drain valve may be an overpressure valve, which is arranged to open at a predetermined working-fluid pressure.
• the drain valve In its activated state, when a signal is being supplied to it, the drain valve may be closed to fluid flow, and in its non-activated state, when it is not receiving any signal, it may be open to fluid flow.
• a "normally open" fluid valve contributes to increased safety in that, in the event of a signal drop-out, it will drain the high-pressure path so that the expander stops.
• a method for the operational and safety control of a heat engine which has a working-fluid path including a high- pressure path and a low-pressure path, the heat engine using a condensable working fluid which is in the liquid phase at least in part of the high-pressure path, and the method including the following steps:
• the heat engine with a fluid-drainage path which is selectably open or closed, and which is connected to a portion of the high-pressure path in which the working fluid is mainly in the liquid phase;
• the method may more specifically include providing the fluid-drainage path with a drain valve and driving the drain valve into the open position when there is a need to drain fluid from the high-pressure path.
• the method may more specifically include:
• the method may further include connecting the fluid-drainage path to the low- pressure path and letting working fluid be drained from the high-pressure path into the low-pressure path.
• the method may more specifically include:
• recuperator does not constitute a necessary component, but is often used to increase the efficiency of a heat engine.
• the method and the device according to the invention give markedly increased safety in a possible fault condition and are arranged to prevent unfortunate or dangerous situations in general. In addition, they are an effective means of stopping the heat engine in a quick, but controlled manner.
• Figure 1 shows a block diagram of a heat-engine system including a heat engine, a heat source, a heat sink, an energy converter and an external control unit, in which interfaces between the components are shown;
• FIG. 2 shows a block diagram of a heat-engine system as shown in figure 1, in which the energy, electricity and signal flows are indicated;
• FIG. 3 shows schematically a heat engine in accordance with the invention with the associated main components
• Figure 4 shows schematically the heat engine of figure 3, but the expander has been specified as being a piston engine.
• the reference numeral 1 indicates a heat engine, which is connected via a heat-source interface 2 to a heat source 4, via a heat-sink interface 6 to a heat sink 8, via a power/electricity interface 10 to an electric-power converter 12 and via a signal interface 14 to an external control unit 16.
• the heat engine 1 preferably forms part of an ORC system and includes a fluid pump 20 with an inlet 22 and an outlet 24. From the outlet 24, a pressure-pump line 26 extends via a recuperator 28 and on to a heater 30.
• the recuperator 28 may consist of an, in the main, standard heat exchanger known per se, with two conventional opposite heat-exchanger sides, not shown, consisting of separate and heat-communicating internal fluid paths.
• the heater 30 typically includes an evaporator 32 and a superheater 34. The heater 30 is supplied with heat Q H from the heat source 4 via the heat interface 2.
• a steam line 36 is connected between the superheater 34 and the inlet 40 of an expander 38.
• the expander 38 may consist of, for example, a turbine, a piston engine or the like.
• An outlet 42 from the expander 38 constitutes an exhaust outlet.
• the components between the fluid pump 20 and the expander 38, including the pressure-pump line 26, the high-pressure side of the recuperator 28, the heater 30 and the steam line 36 constitute the high-pressure path 44 of the heat engine 1.
• the expander 38 drives a generator 48 via a shaft 46. Electric power P EL is transferred via the power/electricity interface 10 to the electric- power converter 12.
• a motor-control unit 50 controls the expander 38 and the generator 48 among other things. Necessary transmitters and control lines, known per se, are not shown.
• An outlet line 52 extends from the outlet 42 of the expander 38, via the recuperator 28, a condenser 54 to a working-fluid reservoir 56.
• the condenser 54 delivers residual heat Qc to the heat sink 8 via the heat-sink interface 6.
• a suction line 58 connects the working-fluid reservoir 56 to the inlet 22 of the fluid pump 20.
• the components between the expander 38 and the fluid pump 20, including the outlet line 52, the low-pressure side of the recuperator 28, the condenser 54, the working-fluid reservoir 56 and the suction line 58 constitute the low-pressure path 60 of the heat engine 1.
• a fluid-drainage path 62 which is here connected to the pressure-pump line 26 between the recuperator 28 and the heater 30, is connected via a drain valve 64 to the outlet line 52 between the expander 38 and the recuperator 28.
• the fluid-drainage path 62 is arranged to short-circuit the high-pressure path 44 with the low-pressure path 60 whenever necessary.
• the drain valve 64 is of an actively controllable kind, like an electromagnetically, mechanically, pneumatically or hydraulically activated on-off valve. Alternatively it may be a proportional valve or a servo-valve, for example.
• the working fluid is first pumped through the recuperator 28, in which it is preheated by receiving residual heat from the exhaust which is flowing out of the outlet 42 of the expander 38 and which is directed into the low-pressure side of the recuperator 52 via the outlet line 52.
• the working fluid After first having passed through the recuperator 28, the working fluid flows into the heater 30 and, in the first step, into the evaporator 32 where it is heated up towards the boiling point and thereby evaporated . Further, the working fluid passes into the superheater 34 where the temperature is increased beyond the boiling point. After that, the working fluid is carried into the expander 38 where part of the added heat energy is converted into mechanical energy by the working fluid being expanded near- adiabatically, near-isothermally, near-isobarically or near-polytropically.
• the mechanical energy is in turn converted into electric energy by means of the generator 48.
• the electric energy from the generator 48 is transferred as electric power PEL from the generator 48 via the power/electricity interface 10 to the electric-power converter 12.
• the expanded working fluid which may now be defined as exhaust, is carried via the outlet line 52 to the low- pressure side of the recuperator 28, where part of the residual heat is returned to the working fluid in the high-pressure path 44 and recovered .
• the working fluid is then directed into the condenser 54 in which the last portion of residual heat Qc that is to be removed flows via the heat-sink interface 6 to the heat sink 8.
• the working fluid is thereby condensed to the liquid phase before it is carried into the working-fluid reservoir 56.
• the motor-control unit 50 may drive the drain valve 64, by means of known control principles, into the open state by a control signal being communicated via a control-signal conductor 66 which is connected to a d rain-valve actuator 68, which in turn ensures that the drain valve 64 takes the open position . There is thereby a short-circuiting, in terms of fluid flow, between the high-pressure path 44 and the low-pressure path 60.
• the heat engine 1 is provided with various known sensors, not shown, so that exactly these conditions can be registered and identified by the motor-control unit 50, which in turn may communicate the necessary control signals, and then in particular the control signal that ensures opening of the drain valve 64.
• working fluid When short-circuiting then takes place, working fluid will be drained from the high- pressure path 44 in a position in which, normally, it is mainly in the liquid phase, up to the point when the entire liquid fraction has been evacuated almost completely.
• the greater portion of the mass of the working fluid will initially be drained in the liquid phase, and subsequent evacuation will then, in the main, consist of working fluid in gaseous form, either as saturated or superheated gas, representing only a minor mass fraction in relation to the total mass of the working fluid.
• the fluid-drainage path 62 is shown connected to the high-pressure path 44 between the recuperator 28 and the heater 30.
• the fluid in the high-pressure path 44 is mainly in the liquid phase between the fluid pump 20 and the heater 30. This part of the high-pressure 44 thus constitutes a portion 74 in which the working fluid is, in the main, in the liquid phase.
• the expander 38 consists of a piston engine.
• the expander 38 is formed with at least one controlled inlet valve 76 and at least one controlled outlet valve 78 which together control the fluid flow through the expander 38, by the valves 76, 78 controlling the fluid flow through the at least one inlet 40 and the at least one outlet 42.
• the controlled valves 76, 78 ensure that said paths are never open simultaneously. Thereby there will not be a direct fluid short-circuiting across the expander 38 if the expander 38 should stop, whereby a direct short-circuiting between the high-pressure path 44 and the low-pressure path 60 is prevented from occurring through the expander 38.
• the inlet valve 76 and the outlet valve 78 are controlled by respective valve actuators 80, and these will normally be synchronized in such a way that this form of short-circuiting is prevented.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Engine Equipment That Uses Special Cycles (AREA)
• Fluid-Pressure Circuits (AREA)
• Output Control And Ontrol Of Special Type Engine (AREA)

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Publications (1)

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Citations (5)

Family Cites Families (17)

• 2013
  • 2013-02-19 NO NO20130277A patent/NO335230B1/no unknown
• 2014
  • 2014-02-17 EP EP14754834.1A patent/EP2959144B1/en active Active
  • 2014-02-17 CN CN201480009535.3A patent/CN105074186A/zh active Pending
  • 2014-02-17 ES ES14754834T patent/ES2947816T3/es active Active
  • 2014-02-17 US US14/767,415 patent/US20160017757A1/en not_active Abandoned
  • 2014-02-17 WO PCT/NO2014/050023 patent/WO2014129909A1/en active Application Filing
  • 2014-02-17 KR KR1020157024054A patent/KR20150117688A/ko not_active Application Discontinuation
  • 2014-02-17 JP JP2015557969A patent/JP6239008B2/ja active Active

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