WO2015040279A1

WO2015040279A1 - An energy converter

Info

Publication number: WO2015040279A1
Application number: PCT/FI2014/050715
Authority: WO
Inventors: Teemu TURUNEN-SAARESTI; Pekka RÖYTTÄ; Juha Jaakko PYRHÖNEN; Jussi HEINIMÖ; Hannu Helmer TERVONEN
Original assignee: Visorc Oy
Priority date: 2013-09-19
Filing date: 2014-09-18
Publication date: 2015-03-26
Also published as: DE212014000185U1; FI20130266L; AT15009U1

Abstract

An energy converter comprises functional elements that comprise at least the fol lowing: an electrical turbo-machine (101) for converting energy contained by va porized working fluid into electrical energy, condenser (102) for condensing the vaporized working fluid outputted by the electrical turbo-machine, and a feed pump (103) for pumping the condensed working fluid to a vaporizer. The energy con verter can be based on for example the Organic Rankine Cycle. The energy con verter further comprises a frame element (140) arranged to act as a mechanical support frame for the functional elements. Furthermore, the piping between the functional elements is at least partly implemented as ducts of the frame element. Therefore, the mechanical structure of the energy converter can be compact, ro bust, and cost effective to manufacture.

Description

An energy converter

Field of the invention

The invention relates generally to energy converters for converting thermal energy into electricity. More particularly, the invention relates to a mechanical construction of an energy converter that can be based on, for example but not necessarily, the Organic Rankine Cycle "ORC".

Background

Small-size energy converters, which can be based on for example the Organic Rankine Cycle "ORC" process, can be used for converting the thermal energy of waste heat into electricity which is easily used for different purposes. The waste heat can be received from various heat-producing processes or heat-producing machines, e.g. a combustion engine or a gas turbine, where, due to the temperature of the waste heat and/or due to the circumstances of the environment, the waste heat cannot be used as such or by means of conventional heat exchangers or corresponding means.

It can be shown thermodynamically that the ORC process is an applicable technique for this kind of energy conversion. The heat of vaporization of organic working fluid is low in relation to e.g. the heat of evaporation of water, and its fall of specific enthalpy in the turbine is small and the mass flow rate in relation to the output is high, wherein it is possible to reach high turbine efficiency even in a range of small capacity. The utilization of high-speed technology, wherein the turbine is directly coupled with a generator rotating at the same speed and thus producing high-frequency current, has made it possible to further simplify the process in a way that e.g. a separate reduction gear required by conventional processes is not needed. Also, the high speed technology makes it possible to provide a hermetic process, which means significant savings in the operational expenses.

Publication EP0090022 describes an energy converter that comprises a vaporizer, i.e. a boiler, a radial turbine, a condenser, a feed pump, and a high-speed genera- tor. The energy converter may further comprise a recuperator and a pre-feeding pump. The thermal energy supplied to the vaporizer is arranged to maintain the Organic Rankine Cycle process driving the generator and thus producing electricity. The radial turbine and the feed pump are directly connected to the rotor of the generator. The rotor is rotatably carried with gas-dynamic bearings utilizing the organic working fluid in gaseous form. The back-surface of the radial turbine is arranged to serve as one abutment surface of a gas-static thrust bearing.

Energy converters of the kind described above are, however, not free from challenges. One of the challenges is related to the fact that an energy converter of the kind described above comprises complex piping system for transferring gaseous and liquid form substances and many heat exchanging elements. Manufacturing, in particular, the complex piping system can be expensive also in serial production.

Summary The following presents a simplified summary in order to provide a basic understanding of some embodiments of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

In accordance with the invention, there is provided a new energy converter that can be based on, for example but not necessarily, the Organic Rankine Cycle "ORC" process. An energy converter according to the invention comprises functional elements that comprise at least the following: - an electrical turbo-machine for converting energy contained by vaporized working fluid into electrical energy,

- a condenser for condensing the vaporized working fluid outputted by the electrical turbo-machine, and

- a feed pump for pumping the condensed working fluid to a vaporizer. The energy converter further comprises a frame element that is arranged to act as a mechanical support frame for the functional elements. Furthermore, a piping between the functional elements is at least partly implemented as ducts of the frame element. The frame element is advantageously a single piece of material which can be manufactured for example by casting, extruding, or laser sintering. Each duct of the frame element can be e.g. a bore made to the frame element or a duct made during e.g. a casting, extruding, or laser sintering process for manufacturing the frame element. Therefore, the mechanical structure of the energy converter can be compact, robust, and cost effective to manufacture. In addition to the above-mentioned turbo-machine, condenser, and feed pump, the functional elements installed in the frame element may comprise a vaporizer, a recuperator, a condenser tank, a frequency converter, a pre-feeding pump, a valve system, and/or instrumentation related to control and/or protection.

A number of non-limiting and exemplifying embodiments of the invention are de- scribed in accompanied dependent claims.

Various exemplifying embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in connection with the accompanying drawings. The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does as such not exclude a plurality.

Brief description of the figures

The exemplifying embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figure 1 a shows a schematic block diagram of an energy converter according to an exemplifying embodiment of the invention, figure 1 b shows a perspective view of the energy converter illustrated in figure 1 a, and figure 1 c shows a view of a section taken along the line A - A shown in figure 1 b. Description of exemplifying embodiments

Figure 1 a shows a schematic block diagram of an energy converter according to an exemplifying embodiment of the invention. Figure 1 b shows a perspective view of the energy converter, and figure 1 c shows a view of a section taken along the line A - A shown in figure 1 b. The section plane is parallel with the xy-plane of a coordinate system 199. The energy converter is advantageously an Organic Ran- kine Cycle "ORC" energy converter that uses suitable organic fluid as the working fluid. The organic fluid can be, for example but not necessarily, one of the silox- anes. It is also possible that the energy converter uses suitable non-organic fluid as the working fluid. The energy converter comprises a frame element 140 shown in figures 1 b and 1 c. In this exemplifying case, the frame element is advantageously a single piece of suitable cast material which can be e.g. aluminum or steel. The frame element 140 is arranged to act as a mechanical support frame for functional elements of the energy converter. In conjunction with some of the func- tional elements, the frame element may also act as a part of these functional elements. For example, the frame element may constitute an outer casing of a heat exchanging element so that the heat exchanging element can be manufactured by installing the inner parts of the heat exchanging element into a suitable cavity of the frame element. The piping between the functional elements is at least partly implemented as ducts of the frame element. Each duct of the frame element can be e.g. a bore made to the single piece of cast material or a duct made during the casting process of the frame element 140. Flanges at the ends of the frame element 140, such as a flange 141 , can be sealed with e.g. O-ring seals, such as an O-ring seal 142, so as to provide a hermetic structure. The functional elements of the energy converter are explained below with reference to the block diagram shown in figure 1 a. The functional elements are denoted in figure 1 c with the same figure reference numbers as in figure 1 a. However, array of functional elements can be different from that shown in Fig 1 b and 1 c. The energy converter comprises an electrical turbo-machine 101 , see figures 1 a and 1 c, for converting energy contained by vaporized working into electrical energy. The electrical turbo-machine 101 is advantageously a high-speed machine whose rotational speed can be as high as e.g. 10000...60000 rpm. The electrical energy outputted by the electrical turbo-machine 101 is supplied to a power grid 150 with the aid of a frequency converter 106. The cable connecting the frequency converter 106 to the power grid is denoted with a reference number 1 14 in figures 1 a-1 c. A vaporizer, i.e. a boiler, 1 17 which vaporizes the working fluid can be operated by e.g. waste heat 127 received from a heat-producing process or a heat- producing machine, e.g. a combustion engine. In the exemplifying case illustrated in figures 1 a-1 c, the energy converter comprises a piping interface 1 12a, 1 12b for connecting to the vaporizer 1 17 which is not an integral part of the energy converter but an external element. In an energy converter according to another exemplifying embodiment of the invention, the vaporizer is an integral part of the energy converter and the vaporizer is implemented within the frame element of the energy converter.

The electrical turbo-machine 101 comprises a generator section 1 18 and a turbine section 1 19. A feed pump 103 for pumping the working fluid to the vaporizer is integrated with the electrical turbo-machine 101 . The generator section 1 18 comprises a stator and a rotor for magnetically interacting with the stator. The stator comprises a stator core structure having a plurality of stator teeth and stator slots, and a stator winding having a plurality of stator coils. The rotor of the generator section may comprise permanent magnets for producing a magnetic flux penetrating the air-gap between the rotor and the stator. In this case, the generator section is capable of operating as a permanent magnet synchronous generator "PMSG". It is also possible that the rotor comprises electrically conductive structures so that the generator section is capable of operating as an asynchronous generator. The turbine section 1 19 comprises a diffuser, a stator nozzle ring, and a first impeller suitable for operating as a turbine for rotating the rotor of the generator section. The feed pump 103 comprises a second impeller for pumping the working fluid. In the exemplifying energy converter illustrated in figures 1 a-1 c, the first and second impellers are directly coupled to the rotor of the generator section. The stator noz- zle ring, the impeller, and the diffuser of the turbine section 1 19 are advantageously suitable for operating as a radial turbine stage whose degree of reaction is less than 50 % e.g. 30 %. Thus, the axial height of the impeller vanes can be increased and, as a corollary, the ratio of the axial clearance to the axial height of the stator and impeller can be made smaller, and thus the efficiency can be improved. The degree of reaction or reaction ratio is defined as the ratio of the static enthalpy drop in the impeller to the static enthalpy drop in the whole turbine stage. The impeller of the feed pump 103 can be, for example, a straight vane radial impeller of a "Barske"-type partial emission pump. The impeller of the feed pump can be provided with a screw-type inducer for reducing the risk of cavitation on the vanes of the impeller, and thereby to reduce the required pre-supply pressure.

The energy converter comprises a condenser 102 for condensing the vaporized working fluid outputted by the electrical turbo-machine 101 , and a feed pump system for pumping the condensed working fluid to the vaporizer 1 17. In the exemplifying energy converter illustrated in figures 1 a-1 c, the feed pump system compris- es the above-mentioned feed pump 103, a pre-feed pump 1 15, and an ejector 1 16 for supplying the pre-feed pump and operated by the output flow of the feed pump 103. In a typical energy converter of the kind described here and having output power about 10 kW, the height hi of the heat exchanger structure of the condenser 102 can be e.g. about 150 mm, the width w1 can be e.g. about 660 mm, and the depth in the z-direction of the coordinate system can be e.g. about 330 mm.

In the exemplifying case illustrated in figures 1 a-1 c, the energy converter comprises ducts 107 for conducting the working fluid to the bearings of the electrical turbo- machine 101 so as to lubricate the bearings with the working fluid. Furthermore, the energy converter illustrated in figures 1 a-1 c comprises a condenser tank 105 for storing the condensed working fluid. An energy converter according to another exemplifying embodiment of the invention comprises a piping interface for con- necting to an external condenser tank that is not an integral part of the energy converter.

The exemplifying energy converter illustrated in figures 1 a-1 c comprises a recuperator 104 for increasing the efficiency of the energy conversion. The recuperator is a heat exchanging element arranged to transfer heat energy from the vaporized working fluid outputted by the electrical turbo-machine 101 to the condensed working fluid outputted by the feed pump 103 and being supplied to the vaporizer 1 17. In a typical energy converter of the kind described here and having output power about 10 kW, the height h2 of the heat exchanger structure of the recuperator 104 can be e.g. about 120 mm, the width w2 can be e.g. about 400 mm, and the depth in the z-direction of the coordinate system can be e.g. about 370 mm.

The exemplifying energy converter illustrated in figures 1 a-1 c further comprises first cooling ducts 108 for conducting cooling fluid, e.g. water, to and from the electrical turbo-machine 101 and second cooling ducts 109 for conducting cooling fluid to and from the condenser 102. As illustrated in figure 1 a, the first and second cooling ducts constitute mutually parallel flowing paths for the cooling fluid. The first and second cooling ducts can be connected to an external cooling fluid circulation system with the aid of a piping interface 1 10a, 1 10b. However, this is only an example of cooling arrangement of the electrical turbo-machine 101 . It may be cooled also otherwise.

Furthermore, the exemplifying energy converter illustrated in figures 1 a-1 c comprises a turbine valve 125 and possibly other control and/or safety instrumentation.

The specific examples provided in the description given above should not be construed as limiting. Therefore, the invention is not limited merely to the embodiments described above.

Claims

What is claimed is:

1 . An energy converter comprising functional elements that comprise at least the following:

- an electrical turbo-machine (101 ) for converting energy contained by vapor- ized working fluid into electrical energy,

- a condenser (102) for condensing the vaporized working fluid outputted by the electrical turbo-machine, and

- a feed pump (103) for pumping the condensed working fluid to a vaporizer, characterized in that the energy converter further comprises a frame element (140) arranged to act as a mechanical support frame for the functional elements, and that a piping between the functional elements is at least partly implemented as ducts of the frame element.

2. An energy converter according to claim 1 , wherein the functional elements further comprise the vaporizer.

3. An energy converter according to claim 1 , wherein the energy converter comprises a piping interface for connecting to the vaporizer.

4. An energy converter according to any of claims 1 -3, wherein the functional elements further comprises a recuperator (104) for transferring heat energy from the vaporized working fluid outputted by the electrical turbo-machine to the con- densed working fluid outputted by the feed pump.

5. An energy converter according to any of claims 1 -4, wherein the functional elements further comprises a condenser tank (105) for storing the condensed working fluid.

6. An energy converter according to any of claims 1 -4, wherein the energy con- verter comprises a piping interface for connecting to an external condenser tank for storing the condensed working fluid.

7. An energy converter according to any of claims 1 -6, wherein the functional elements further comprise a frequency converter (106) for supplying the electrical energy outputted by the electrical turbo-machine to an external electrical system.

8. An energy converter according to any of claims 1 -7, wherein the energy con- verter comprises ducts (107) for conducting the working fluid to bearings of the electrical turbo-machine so as to lubricate the bearings of the electrical turbo- machine with the working fluid.

9. An energy converter according to any of claims 1 -8, wherein the energy converter comprises first cooling ducts (108) for conducting cooling fluid to and from the electrical turbo-machine and second cooling ducts (109) for conducting the cooling fluid to and from the condenser, the first and second cooling ducts constituting mutually parallel flowing paths for the cooling fluid.

10. An energy converter according to any of claims 1 -9, wherein the working fluid is organic working fluid.

1 1 . An energy converter according to any of claims 1 -10, wherein the frame element (140) is a single piece of material made by one of the following manufacturing methods: casting, extruding, or laser sintering.