Patent Application
20160032786
The present invention refers to a plant, for example a Rankine cycle plant, for generating electric and/or mechanical power by recovering and converting heat.
The present invention can find an application for example in biogas/biomass plants for recovering waste heat of a cogeneration process, in geothermal plants for harnessing medium/small heat sources, in industrial plants for recovering waste heat (by converting the waste heat of the industrial processes), in the domestic environment for producing electric power and harnessing the heat for sanitary use. A further use of the plant can refer to systems, both domestic and industrial systems, wherein the heat source is provided by plants absorbing solar power. Further, it is possible to provide applications of the plant in the automotive field, for example for recovering the heat from the engine (water and/or fumes).
As it is known, heat sources are widely available, particularly at a low/medium temperature, which are now dispersed in the environment, and therefore wasted. De facto, the conversion of the heat supplied by said sources into electric power is, by the nowadays available recovering and converting means and processes, too expensive in relation with the power produced. Therefore, such sources, even though are used in a limited way for professional applications, are scarcely used by the people, and particularly in the domestic environment.
The most common heat sources, which here it is preferentially made reference to, are available both as a by-product of the human activity and in nature, such as for example the heat contained in the waste industrial products or the heat contained in the biomasses if the latter are combusted.
Several applications of the Rankine cycle for recovering thermal power and the consequent production of electric power are known. The preferred embodiment consists of using, as expansion chamber, a turbine. However, such solution has some constraints and disadvantages which are well known to the person skilled in the art, and which are:
For the above mentioned reasons, it is absolutely evident that the steam turbines are not very suitable for harnessing medium/low temperature thermal sources and having an extremely variable thermal supply (as indicated in the above exemplified examples) and therefore not very suitable for small-sized plants (having a supplied electric power less than 50 KW, for example).
From documents JP 10252558, JP 10252557 and JP 10259966, some known different technical solutions using the Rankine cycle for different objects are known; however, none of the suggested solutions is particularly advantageous for generating electric power, particularly if the thermal power is supplied under an extremely variable range.
In order to overcome the above described disadvantages, it is known to use alternate or rotative volumetric expanders. Such expanders are capable of operating under relatively modest fluid flow rates without excessively reducing the power and efficiency. Further, volumetric expanders, operating at smaller thermal powers, operate at a number of revolutions (cycles) substantially smaller than the turbines rotation speeds eliminating in this way the risk of damaging the movable parts in case the liquid (drops formed by an incorrect vaporization of the working fluid) flows into the expansion chamber. Further, the above described volumetric expanders have a structural complexity smaller than the one of the turbines, with a consequent reduction of the costs.
Besides a reduced complexity, volumetric expanders are extremely more compact than the turbines, which in turn makes easier their implementation, and assembly.
An example of a volumetric expander used for converting thermal power in electric power by means of low temperature heat sources, is described in the patent application U.S. 2012/0267898 A1 of the Applicant.
Such application describes a Rankine cycle machine comprising a cylinder and an associated piston adapted to alternately move inside said cylinder. To the piston is associated a main shaft which, in turn, is connected to a DC voltage generator formed by a rotor and a stator: the rotor is connected to and actuated by the main shaft. The cylinder is provided with an intake port and a discharge port which the working fluid flows through. For actuating the piston, the machine uses a rotative valve enabling the desired sequence among the steps of introducing, expanding, and discharging the fluid. In order to synchronize such steps to each other, the rotative valve is actuated by a plurality of motion transmission members connected to the main shaft.
Despite the described solutions (volumetric expanders) are, under conditions of low temperature heat sources, enhancing in comparison with the turbines, the above described volumetric expanders are not devoid of disadvantages. Particularly, the Applicant believes the known volumetric expanders, and also the machine described in patent application U.S. 2012/0267898 A1 of the Applicant, are further improvable under different aspects.
A first object of invention consists of providing a plant, for example a Rankine cycle, which can be adapted to different working conditions in order to effectively harness the available heat sources and supply the maximum power with excellent efficiencies.
A further main object of the invention consists of making available a plant, for example a Rankine cycle, which is suitable for operating for long periods of time without requiring any maintenance and embodying a highly integrated and compact unit.
It is a further object of the invention to make available a plant, for example a Rankine cycle, which is simple to be manufactured and easy to be installed and consequently showing extremely reduced production, maintenance and assembly costs.
Lastly, it is an object of the invention to develop a process capable of efficiently harnessing the above mentioned plant.
One or more of the above described objects which will be better understood in the following description, are substantially met by a Rankine cycle plant according to one or more of the attached claims.
Aspects of the invention are herein described in the following.
In a 1st aspect, it is provided a closed cycle plant (1), particularly a Rankine cycle, for converting thermal power in electric power, comprising:
a closed circuit (2), inside which at least one working fluid circulates according to a predetermined circulation direction,
In a 2nd aspect according to aspect 1, the plant (1) comprises:
In a 3rd aspect according to anyone of the preceding aspects, the regulation device (14) comprises at least one mask (15) movable relatively to the inlet (8) for enabling the variation of the the maximum cross-section and determining a regulation of the volumetric flow rate of the working fluid entering the expansion chamber (7) during the introduction condition.
In a 4th aspect according to the preceding aspect, the valve (10) comprises:
In a 5th aspect according to the preceding aspect, the mask (15) is interposed between the first cavity (31) of the distribution body (28), and the first passage (26) of the valve (10), the mask (15) being movable relatively to the first passage (26), particularly relatively to the inlet (8), for determining a variation of said maximum cross-section.
In a 6th aspect according to aspect 4th or 5th, the mask (15) comprises a semi-cylindrical sleeve interposed between the housing seat (25) and the distribution body (28), the mask (15) being rotatively movable around the rotation axis of the distribution body (28).
In a 7th aspect according to anyone of aspects from 3rd to 6th, the mask (15), following its own angular movement, determines a predetermined number of occlusion degrees of the inlet (8), each occlusion degree being defined by the ratio of the area of the maximum cross-section of the inlet (8) without the mask (15) to the area of the maximum passage cross-section in the presence of the mask (15).
In an 8th aspect according to the preceding aspect, the occlusion degree being comprised between 1 and 3, particularly between 1 and 2, still more particularly between 1 and 1.5
In a 9th aspect according to anyone of aspects from 3rd to 8th, the regulation device (14) comprises:
In a 10th aspect according to anyone of aspects from 3rd to 9th, the regulation device (14) comprises at least one first pusher (44) connected, at one side, to a terminal portion of the mask (15), and at another side, to the valve body (24), said pusher (44) being configured to move relatively to the valve body (14) for displacing the mask (15), relatively to the inlet (8), into a plurality of operative positions.
In an 11th aspect according to the preceding aspect, the regulation element (14) comprises at least one second pusher (45) connected, at one side, to a terminal portion of the mask (15), and at another side, to the valve body (24), said second pusher (45) being placed on the opposite side of the first pusher with reference to the mask (15) and being configured to define a condition blocking the mask (15) following the movement of the latter in a predetermined operative position.
In a 12th aspect according to the preceding aspect, each of said first and second pushers (44; 45) comprises at least one screw arranged to push the mask (15) at a terminal end following a relative rotation of the screw with respect to the valve body (24).
In a 13th aspect according to aspect 11th or 12th, at least one of said first and second pushers (44; 45) comprises a hydraulic or pneumatic actuator connected to the control unit (33), said control unit (33) being configured to send a command signal to the actuator for determining a relative displacement of the mask (15) with respect to the inlet (8).
In a 14th aspect according to anyone of the aspects from 4th to 13th, the distribution body (28) is actuated by at least one motion transmission element connected to the main shaft (11) and configured to maintain synchronized the rotation of the distribution body (28) to the rotation of the main shaft (11).
In a 15th aspect according to anyone of the preceding aspects, the volumetric expander (4) comprises an alternate volumetric expander, wherein the expansion chamber (7) has a hollow cylindrical seat (22), while the active element (6) comprises a piston (23) countershaped to the seat (22) of the expansion chamber (7) and slidingly moveable inside the latter, or wherein the volumetric expander (4) is a rotative volumetric expander, wherein the expansion chamber (7) has a seat (22) having an epitrochoidal shape with at least two lobes, while the active element (6) comprises a piston (23) rotatively movable inside the seat.
In a 16th aspect according to anyone of aspects from 2nd to 15th, the plant comprises at least one second heat exchanger (16) active on the circuit (2) and interposed between the expander (4) and pump (13), said second heat exchanger (16) being suitable for receiving through the working fluid exiting said expander (4), said second heat exchanger (16) being configured to communicate with a cold source (C) and enable to condensate the working fluid until it is caused a complete passage from the gaseous state to the liquid state.
In a 17th aspect according to the preceding aspect, the plant comprises at least one collecting tank (17) active on the circuit (2) and interposed between the pump (13) and second exchanger (16), said collecting tank (17) being configured to contain the working fluid at the liquid state exiting said second exchanger (16).
In an 18th aspect according to the preceding aspect, the pump (13) is connected to the collecting tank (17) and being suitable for sending the working fluid at the liquid state, towards the first heat exchanger (3).
In a 19th aspect according to anyone of aspects from 2nd to 18th, the plant comprises at least one third heat exchanger (18) operatively active on the circuit (2) upstream of the first heat exchanger (3) and suitable for receiving through said working fluid, said third heat exchanger (18) being further configured to receive heat from a hot source (H) and enable to pre-heat the working fluid before introducing the latter in the first heat exchanger.
In a 20th aspect according to the preceding aspect, the third heat exchanger (18) is configured to pre-heat the working fluid until a saturated liquid condition.
In a 21st aspect according to the aspect, the first heat exchanger (3) is suitable for receiving the working fluid in a saturated liquid condition and for supplying at the outlet the working fluid in a saturated vapor condition.
In a 22nd aspect according to anyone of aspects from 19th to 21th , the first and third heat exchangers (3; 18) are positioned immediately and consecutively after each other according to a working fluid circulation direction, said first and third heat exchangers (3; 18) being configured to receive heat from the same hot source (H).
In a 23rd aspect according to anyone of aspects from 19th to 22th, the plant (1) comprises a heating circuit (19) extending between and inlet (20) and an outlet (21) and inside which at least one heating fluid from said hot source (H) is suitable for circulating, said first and third heat exchangers (3; 18) being operatively active on the heating circuit (19), and interposed between the inlet (20) and outlet (21) of said circuit (19), the heating fluid, circulating from the inlet (20) towards the outlet (21), consecutively flowing through the first and third heat exchangers (3; 18).
In a 24th aspect according to the preceding aspect, the heating fluid entering the first heat exchanger (3) has a temperature less than 150° C., particularly comprised between 25° C. and 100° C., still more particularly between 25° C. and 85° C.
In a 25th aspect according to anyone of aspects from 17th to 24th, the pump (13) is positioned downstream the volumetric expander (4) with respect to the working fluid circulation direction, particularly interposed between the collecting tank (17) and the first heat exchanger (3).
In a 26th aspect according to anyone of aspects from 2nd to 25th, the pump (13) is configured to impose a pressure jump to the working fluid, comprised between 4 bar and 30 bar, particularly between 4 and 25 bar, still more particularly between 7 bar and 25 bar.
In a 27th aspect according to anyone of the preceding aspects, the plant comprises, as a working fluid, at least one organic-type fluid.
In a 28th aspect according to the preceding aspect, the organic fluid of the working fluid is present by a percentage comprised between 90% and 99%, particularly between 95% and 99%, still more particularly about 98%.
In a 29th aspect according to aspect 27th or 28th, the organic fluid comprises at least one selected in the group of the following fluids: R134A, 245FA, R1234FY, R1234FZ.
In a 30th aspect according to anyone of the preceding aspects, the plant comprises, as a working fluid, an organic fluid comprising one or more hydrocarbons, preferably halogenated hydrocarbons, still more preferably fluorinated hydrocarbons, said working fluid having:
In a 31st aspect, it is provided a process for converting thermal power in electric power, comprising the following steps:
In a 32nd aspect according to the preceding aspect, the step of regulating the flow rate of the working fluid comprises a relative movement of the mask (15) for varying the maximum passage cross-section of the working fluid entering the expansion chamber (7).
In a 33rd aspect according to aspect 31st or 32nd, the regulating step comprises at least the following sub-steps:
In a 34th aspect according to anyone of aspects from 31st to 33rd, the process comprises at least one step of condensing the working fluid exiting the expander (4) by the second heat exchanger (16), the process further comprises a step of collecting the working fluid condensated inside the collecting tank (17), the step of sending the working fluid to the first exchanger, comprises a sub-step of withdrawing the working fluid at the liquid state present inside the collecting tank (17) by the pump (13).
In a 35th aspect according to anyone of aspects from 31st to 34th, the step of heating the working fluid, enables, by the first heat exchanger (3), to bring the latter to a temperature less than 150° C., particularly less than 90° C., still more particularly comprised between 25° C. and 85° C.,
In a 36th aspect according to anyone of aspects from 31st to 35th, the step of heating the working fluid, comprises a sub-step of preheating the working fluid by the third heat exchanger (18) before introducing the latter in the first heat exchanger (3), the preheating step bringing the working fluid to a temperature comprised between 25° C. and 130° C., particularly between 15° C. and 85° C., the heating step enabling to maintain the latter in a saturated liquid condition.
In a 37th aspect according to anyone of aspects from 32nd to 37th, the fluid sending step enables to impose, by the pump (13), a pressure jump to the working fluid comprised between 4 bar and 30 bar, particularly between 4 bar and 25 bar, still more particularly between 7 bar and 25 bar.
Some embodiments and some aspects of the invention will be described in the following with reference to the attached drawings, supplied in an exemplifying and therefore non limiting way, wherein:
With 1 has been generally indicated a closed cycle plant, particularly a Rankine cycle, for converting thermal power in electric power. The plant 1 finds, for example, application in biogas/biomass plants for recovering waste heat of a cogeneration process, in geothermal plants for harnessing medium/small heat sources, in industrial plants for recovering heat waste (conversion of heat waste from industrial processes), in the domestic environment for producing electric power and harnessing the heat for sanitary use. A further use of the plant 1 can regard both domestic and industrial systems, wherein the heat source is provided by systems absorbing solar power. Further applications of the plant in the automotive field, for example for recovering heat from the engine (water and/or fumes), are provided.
As it is visible in
As it is visible for example in the schematic views of
Due to the pressure jump imposed by the pump 13, the working fluid circulates in circuit 2 and particularly exiting from the latter the fluid arrives in a first heat exchanger or vaporizer 3 active on circuit 2. De facto, the working fluid at the liquid state supplied by pump 13, is introduced inside the vaporizer 3 which is configured to heat said fluid until it is caused the passage from the liquid state to the gaseous state. More particularly, the vaporizer 3 is arranged to receive the passing working fluid and further receive heat from a hot source H (
From a structural point of view, the vaporizer 3 can, for example, comprise one heat exchanger suitable for harnessing, as hot source H, a further working fluid supplied by a different industrial plant. Alternatively, the vaporizer 3 can comprise a boiler suitable for enabling the state change of the working fluid by means of a hot source H obtained by combustion.
Following again along the circulation direction of the working fluid, it is possible to observe that the working fluid at the gaseous state exiting the first heat exchanger 3, enters a volumetric expander 4 configured to convert the thermal power of the working fluid in mechanical power (
The volumetric expander 4 comprises at least one jacket 5 housing an active element 6 suitable for defining, in cooperation with said jacket 5, a variable volume expansion chamber 7 (see
Further, the volumetric expander 4 comprises a transmission element 37 connected, at one side, to the active element 6, and at the another side, is associated to a main shaft 11 configured to rotatively move around an axis X (see
As it is visible for example in
A non limiting preferred embodiment of the plant 1 is illustrated in
In the embodiments illustrated in the attached figures, the third heat exchanger 18 consists, in a non limiting way, in a detail distinct (independent) from the economizer 36 and vaporizer 3. Alternatively, the pre-heater 18 could be integrated with the vaporizer 3 to substantially form an “all-in-one” exchanger (this condition is not illustrated in the attached figures); in this last described condition, the plant 1 can comprise only two exchangers (an “all-in-one” exchanger and an economizer 36) or just one exchanger (only the “all-in-one” exchanger) if the heat recovery by the economizer 36 is discarded.
Preferably, the plant 1 comprises at least one heating circuit 19 (
The heating fluid entering the circuit 19, has a temperature less than 150° C., particularly comprised between 25° C. and 130° C. The temperature of the heating fluid is suitable for enabling to vaporize the working fluid. At the outlet of the vaporizer 3, the heating fluid has a temperature less than the temperature of the same entering from said vaporizer: such temperature decrease is caused by the heat released by the heating fluid to the working fluid. Specifically, the heating fluid entering the third exchanger 18, has a temperature less than 100° C., particularly comprised between 20° C. and 90° C.
The first and third heat exchangers 3, 18 are structurally sized so that the working fluid passing from the latter, is maintained in a saturated liquid condition inside the third exchanger 18, while the state change of the working fluid from the liquid to the gaseous state takes place only in the first exchanger 3.
As it is visible in
As it is visible in
Advantageously, the plant 1 comprises a control unit which is connected to the first and second temperature sensors 39, 40 and to the first and second pressure sensors 34, 35. The control unit 33 is configured to receive the control signals of sensors 39 and 34 and determine the temperature of the hot source H at the inlet and at the outlet respectively from the vaporizer 3 and pre-heater 18: in this way, the control unit 33 is capable of monitoring the hot source H and consequently the heat supplied to the exchangers. As said before, further, the control unit 33 is connected to the first and second pressure sensors 34 and 34; said unit 33 is configured to receive the control signals of sensors 34 and 35 for determining the pressure of the working fluid entering and exiting respectively the volumetric expander 4 and pump 13, in other words the maximum and minimum pressure of the circuit 2. In this way, the control unit 33 can monitor the values of the pressure of the working fluid in circuit 2. Preferably, the control unit 33 is further configured to compare the pressure at the inlet of the expander 4 with a predetermined reference value, for example referred to a minimum required pressure value, and determine an intervention or alarm condition in case the measured pressure value is less than the reference value. De facto, the monitoring executed by the control unit is for setting/controlling the difference between the saturation temperature and the working temperature of the fluid, in other words for determining if the working fluid is in a saturated vapor condition or is still in a phase change (the change from the liquid phase to the gaseous one).
Advantageously, the plant 1 can be provided with a bypass circuit 41 fluidically communicating with the circuit 2 and suitable for enabling to bypass the volumetric expander 4. More particularly, the bypass circuit 41 is connected upstream and downstream of the expander 4 and thanks to the presence of interception elements 42 (solenoid valves) both in the circuit 2 and the bypass circuit 41 it is possible to manage the path of the working fluid and possibly bypass the volumetric expander 4.
Advantageously, the control unit 33 is connected to the interceptionelements 42: due to the pressures monitoring, the control unit 33 is configured to determine a possible intervention condition (as previously described for example a condition wherein the maximum pressure of the working fluid is less than a predetermined limit) and command to bypass the expander until the circulation pressure of the working fluid does not exceed a pre-established level: in this way it is possible to prevent the working fluid from being introduced in the expander 4 at a too low pressure.
A further additional component of the plant in
The volumetric expander 4, according to the present invention, comprises at least one jacket or cylinder 5 housing an active element 6 suitable for defining, in cooperation with the jacket 5, a variable volume expansion chamber 7. The attached figures represent, in a non limiting way, a volumetric expander 4 having a jacket 5 comprising a cylindrical shaped seat 22 inside which a plunger-type piston 23 having also a shape at least partially countershaped (cylindrical) to the seat is slidingly moveable: in this way, the expander 4 defines an alternate-type volumetric expander 4.
In a first embodiment shown for example in
In the just described arrangement, each active element 6 is connected to the same main shaft 11 which is formed by “goose-neck” portions (see
A further embodiment of the plunger expander 4 is shown in
Besides the use of an alternate expander, it is possible to implement a rotative-type expander 4, wherein the expansion chamber 7 has a seat having an epitrochoidal shape with two or more lobes, inside which a rotative piston 23 is rotatively movable.
In a further alternative, the plant 1 can use expanders having a “free pistons” arrangement or can use an expander configured to obtain an exclusively rectilinear alternate motion applied to linear-type generators.
As previously said with reference to the motion transmission from the active element to the main shaft, the expander 4 comprises, independently from the type of the employed expander 4, a transmission element 37 (for example a rod in case of an alternate volumetric expander as shown in
As previously described, the jacket 5 has at least one inlet 8 and one outlet 9 respectively suitable for enabling to introduce and discharge the working fluid, arriving from vaporizer 3, in the expansion chamber 7. The volumetric expander 4 is fluidically communicating with the circuit 2 by said inlet 8 and said outlet 9 which are respectively suitable for enabling to introduce the working fluid into the expansion chamber 7 and then to discharge it.
For determining the movement of each active element 6, the circulation of the working fluid passing from the volumetric expander, particularly from the expansion chamber 7 must be regulated. For this reason, the volumetric expander 4 comprises a valve 10 located, in a non limiting way, outside the expansion chamber 7 (substantially defining the head of the jacket 5) and configured to enable to selectively introduce and discharge the working fluid from the expansion chamber 7. More particularly, the valve 10 is configured to define inside the expansion chamber 7 predetermined operative conditions, such as:
Based on what has been said, it is possible to observe that the working fluid exiting the first heat exchanger or vaporizer 3 has not a direct fluid communication with the working fluid exiting the expander 4 because the flow is interrupted due to the closure of the inlet and outlet by the definition of the expansion condition. The sequence of the above described conditions defines a working cycle of the fluid inside the expansion chamber. By alternating the introduction, expansion and discharge conditions, the valve 10 enables to move the active element 6 inside the jacket (an alternate sliding in case of a piston expander, or a rotation in case of a rotative expander). From this point of view, the expander 4 substantially defines a two-stroke engine executing a complete cycle of introduction and discharge in just only one revolution of the main shaft.
The valve 10, in order to ensure the rotation of the main shaft 11, must synchronize the expansion conditions inside the two jackets 5 so that the latter do not simultaneously occur (timing of the active elements 6).
More particularly, the valve 10 comprises a valve body exhibiting a housing seat 25 having, in a non limiting way, a substantially cylindrical shape. The body 24 of the valve 10 further comprises at least one first and one second passages 26, 27 (
The first and second cavities 31, 32 (
With reference to the exit path of the working fluid from the inside of the chamber 7 to the outside, it is obviously possible to implement a similar solution. From the inside of the chamber 7, the same working fluid can exit by successively flowing through the exit 9, second passage 27, second cavity 32, second channel 30. Moreover, means for commanding the distribution body 28 (rotative valve), are provided which when are combined with the arrangement, size and layout of the described elements, are suitable for causing, for each complete revolution of the main shaft 11, the intake opening 31a to rotate for a short interval, comprised in the same complete revolution, in front of the inlet in order to permanently communicate the chamber 7 of the jacket 5 with the vaporizer 3. In a successive interval of the same rotation, the distribution body 28 closes the inlet 8, and communicates the chamber 7 with the outlet 9. Substantially, the expansion chamber 7 alternately communicates with first and second passages 26 and 27 for introducing and discharging the working fluid, according to a sequence synchronized with the movement and position of the active element 6, and such sequences of opening/closing the inlet 8, and opening/closing the outlet 9 are commanded by, and are comprised in the same and only rotation of, the main shaft 11. Therefore, introducing a working fluid at the gaseous state at a suitable pressure, and under the above explained conditions, inside the expansion chamber 7, accomplishes a predetermined alternate or rotative movement of the active element 6 inside the jacket; such movement transforms such movement in a rotative movement of said shaft 11, which can be used for actuating an electric generator 12, as shown in the attached figures, consisting of a rotor, coupled to said main shaft 11, and a stator, per se known. Therefore, the electric generator 12 generates one or more electric voltages suitable for supplying, by convenient electric connections, not shown, the using devices which can have a wide variety of shapes, uses and types.
As previously said, the plant comprises a control unit 33; advantageously, such unit 33 is connected to the distribution body 28 and/or main shaft 11, and is configured to monitor the position and movement of the latter.
As it is visible in the attached figures, the plant 1 further comprises a regulation device 14 configured to enable to vary at least one of the following parameters: the duration of the introduction condition, the maximum passage cross-section of the inlet 8. Specifically, the regulation device 14 is suitable for managing the volumetric flow rate of the working fluid introducible into the expansion chamber 7, during the introduction condition. De facto, the regulation device 14 enables to manage the step of introduce the working fluid and therefore to regulate also the duration of the isobaric expansion step of the active element 6 (piston). Obviously, the regulations will depend on the size of the active element 6, and particularly on the total stroke of the latter inside the jacket. In a preferred embodiment of the invention, the regulation device 14 comprises at least one mask 15 moveable relative to the inlet 8 to enable to vary the maximum passage cross-section of the latter in order to determine the regulation of the volumetric flow rate of the working fluid entering the expansion chamber 7 during the introduction condition of the valve 10. More specifically, the mask 15 is interposed between the first cavity 31 of the distribution body 28 and first passage 26 of the valve 10: being the mask 15 moveable relatively to the first passage 26, particularly the inlet 8, it enables to vary the passage cross-section of the fluid through the first passage 26 and consequently to vary the volumetric flow rate of the working fluid entering the chamber 7.
The mask 15 comprises, in a non limiting way, a semi-cylindrical sleeve interposed between the housing seat and the distribution body 28. In this arrangement, the mask 15 is rotatively moveable around the rotation axis of the distribution body 28 for placing itself in a plurality of angular positions with respect to the first passage 26. The mask 15 can comprise a semi-cylindrical plate extending between a first and second terminal ends (as shown in the exploded view in
Under both the above described conditions, it is possible to vary a predetermined degree of occlusion of the passage cross-section of the working fluid at the inlet 8. More particularly, the mask 15, following its own angular movement, determines a predetermined number of degrees of occlusion of the inlet 8; each occlusion degree is defined by the ratio of the area of the maximum cross-section of the inlet 8 without the mask 15, to the area of the maximum passage cross-section in the presence of the mask 15. The occlusion degree is comprised between 1 and 3, particularly between 1 and 2, still more particularly between 1 and 1.5. De facto, the movable mask 15 determines, based on the occlusion degrees, the point wherein the gas introduction step ends, which characterizes the successive expansion step. In the preferred illustrated embodiment, the mask 15 has a semi-circular shape; however, it is not excluded the possibility of using a plate-shaped mask extending along a prevalent extension plane and suitable for translating along a predetermined direction between the first passage 26 and first cavity 31.
As it is visible in
To better understand the parameters effective for regulating the mask 15, it is useful to analyze the working cycle of the expander 4. De facto, the working fluid, during the introduction condition, is introduced in the expansion chamber 7 at a predetermined temperature set in the vaporizer 3. Further, the working fluid has a predetermined pressure substantially equal to the pressure of the working fluid exiting the pump 13 (maximum pressure of the circuit 2). Based on the characteristics of the fluid, such as for example, the pressure, temperature and volumetric flow rate, it is possible to obtain a predetermined thrust force on the active element and consequently a predetermined amount of obtainable work. Particularly, the obtainable work is given by the pressure difference between the inlet and the outlet of the expansion chamber 7 for the variable volume of the latter. The pressure of the working fluid entering the expander 4 is the maximum pressure the working fluid attains inside circuits 2 and depends on the characteristics of the pump 13: it is the pump 13 that determines the pressure jump. The pressure of the working fluid exiting the expander 4 is the discharge pressure. In order to maximize the obtainable work, the discharge pressure exiting the expander 4 must be substantially equal to the fluid condensation pressure, in other words, the pressure of the working fluid entering the pump 13, particularly inside the collecting tank 17. It is evident that the volume of the jacket 5 remains constant and consequently for maximizing the obtainable work it is necessary to maximize the pressure jump. As previously said, the maximum pressure in the circuit depends on the characteristic of the pump 13; instead, with reference to the minimum pressure (the condensation pressure) it is a variable parameter depending on the environmental atmospheric conditions.
In order to maximize the obtainable work, with the same maximum pressure suppliable by the pump 13, the discharge pressure at the outlet of expander 4 must be substantially equal to the minimum pressure. The purpose is to increase the power or efficiency of the whole plant. De facto, if at the bottom dead center (BDC) of the active element 6 the pressure of the working fluid (gas) is equal to the one in the condenser, the cycle will have the maximum efficiency because it is harnessed all the expansion step without releasing a surplus heat to the condenser and without having done a negative work in the downward stroke. On the contrary, if the pressure of the working fluid, at the BDC is greater than the one of the condensation, there is a potentially useful lost heat at the outlet of the expander which will be wasted (lost) at the condenser (there is a drop of the efficiency and a loss of power). De facto, if the discharge pressure of the working fluid exiting the expander is greater than the condensation pressure, there will be a waste of power equal to the difference between the latter two pressures.
Moreover, if the working fluid pressure will be less than the condensation pressure before the active element reaches the BDC, the active element 6 (piston) effects a negative work because the latter operates against the system from the position wherein the fluid pressure is equal to the condensation pressure to the BDC: such work is performed by the system on the active element 6 and represents a negative work phase which is subtracted from the overall cycle positive phase (reduction of the power suppliable by the plant 1).
The regulation device 14 is configured to enable to introduce, inside the expansion chamber 7, an amount of working fluid so that, at the end of the expansion condition, the discharge pressure of the latter is substantially equal to the condensation pressure of the working fluid (pressure of the working fluid at the liquid state entering the pump 13). De facto, the regulation device 14 is suitable for enabling the expander 4 to follow the trend of the condensation pressure in order to maximize the obtainable work. In order to perform a dynamic control on the discharge pressure of the expander 4, the plant 1 can use the control unit 33 which, by the sensors 34, 35, 39 and 40, can monitor the pressures and temperatures of the working fluid, and consequently, by means of a connection with the actuating device 43, command the mask 15.
Working Fluid Advantageously, the working fluid used inside the plant 1, comprises at least one organic fluid (ORC fluid). Preferably, the working fluid comprises an amount of organic fluid comprised between 90% and 99%, particularly between 95% and 99%, still more particularly about 98%. The use of an organic fluid is particularly advantageous for the plant due to the excellent capacity of transferring heat from a hot source to a cold source. The organic fluid is mixed with at least an oil configured to enable to lubricate the movable elements of the expander 4 (active element 6); the presence of the oil enables to further improve the sealing and a proper operation of the exchangers. For example, the used organic fluids can comprise at least one selected among the group of the following fluids: R134A, 245FA, R1234FY, R1234FZ.
Moreover, it is an object of the present invention a process for converting thermal power in electric power.
The process comprises a step of circulating the working fluid, whose movement is imparted by the pump 13. The working fluid, propelled by the pump 13, arrives into the vaporizer 3 which, due to the hot source H, heats the working fluid until it is evaporated (condition shown by the scheme in
After the vaporizing step, the working fluid at the gaseous state flows into the volumetric expander 4: the working fluid consecutively flows through the housing seat 25 of valve 10, first channel 29, first cavity 31, opening 31a, first passage 26, inlet 8 until it flows into the expansion chamber 7: such steps determining the working fluid introduction condition. After the introduction step, the expander determines the expansion step (the inlet 8 and outlet 9 are closed and ensuing expansion of the fluid) due to the greater pressure. Due to such expansion, the active element 6 is biased to alternately (alternate expander) or rotatively (rotative expander) move, which is per se known, by putting therefore in rotation the main shaft 11 and ultimately actuates said electric generator 12. The gas flow is therefore expelled from the expansion chamber 7 through the outlet 9, second passage 27, opening 32a, second channel 30 until it exits the body 24 of valve 10.
The process comprises a step of regulating the volumetric flow rate of the working fluid entering the expansion chamber 7 by the regulation device.
The regulation step comprises a step of controlling the evaporation and condensation pressures by the sensors 34 and 35: such sensors send a respective command signal to the control unit 33 which is suitable for processing the signal and determining such pressures. Once the evaporation and condensation pressures have been determined, it is possible to act on the regulation device 14 to determine a discharge pressure of the expander substantially equal to the condensation pressure. More particularly, the regulation step provides to move the mask 15, by the actuating element 43, with respect to the inlet 8 in order to vary the through cross-section of the working fluid for determining the right volumetric flow rate which enables to obtain a discharge pressure equal to the condensation pressure (maximization of the obtainable work). From there, the same circuit 2 conveys the working fluid in the condenser 16 where such fluid is condensed and supplied to the collecting tank 17. The tank 17 fluidically communicates with the pump 13 which withdraws directly from said tank so that the working fluid again circulates in the circuit. More particularly, the collecting tank 17 is interposed between the condenser 16 and pump 13 and enables to collect the working fluid at the liquid state: in such a condition, the tank 17 enables the pump 13 to suction the fluid without suctioning possible air bubbles in order therefore to ensure a continuous supply of the liquid.
The solution of the electric generation plant 1 can be advantageously harnessed under circumstances and in environments which are very different; for example, the hot supply source “H” can be an industrial discharge, while the heat exchanger can use a cold source “C” consisting for example in a watercourse, or an ambient air condenser (case illustrated in
The advantage of the above described solution consists in that the distribution body 28 shows some remarkable and undisputable advantages over the standard distribution by stem valves, which are:
Further, the fact that the distribution body 28 can rotate synchronously with the movement of the active element causes the vaporizer 3 to communicate with the inlet 8, particularly with the expansion chamber in a predetermined position of this element, typically when it reaches anticipated or retarded angles with respect to the upper dead center, which depend on the ratio between the operative pressures, and the chamber is closed after a predetermined fraction of time, before the active element reaches the bottom dead center; a similar situation, although obviously inverted, must be fulfilled also with reference to the opening and closure of the discharge opening 11. So, the main shaft 11 is connected to the distribution body 28 by an assembly of kinematic elements comprising, for example, gears, pinions, idle wheels, suitable for acting on the distribution body 28 in order to ensure the above described conditions. Since the main shaft 11 rotates a complete revolution with a double downward and upward stroke of the actuating element, it will suffice to implement said kinematic elements so that one revolution of the main shaft 11 corresponds to just one revolution of the distribution body, which in turn causes both an opening and closure of the introduction path through the inlet 8, and a successive opening and closure of the discharge path through the outlet 9.
Further, the fact of varying the discharge pressure of the working fluid exiting the expander 4 enables to make available a plant adaptable to different working conditions and consequently suitable for operating in a wide range of operative conditions.
De facto, the possibility of regulating the through cross-section of the working fluid entering the expansion chamber 7 enables to maximize the obtainable work and therefore ensures a certain operability of the plant 1 also under conditions of low thermal available power (a hot source H at a medium/low temperature).
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2013A000375 | Mar 2013 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2014/059635 | 3/11/2014 | WO | 00 |
