Patent Application
20180258799
The invention relates to an apparatus of Organic Rankine Cycle type including a closed loop working fluid circuit operable between a heat source and a heat sink. More specifically the invention relates to ORC apparatuses having a working fluid circuit including: a heat exchanger arrangement for vaporizing and/or superheating a working fluid by exchanging energy from the heat source; at least one turbine for expanding the vaporized/superheated working fluid; condensing means connectable to the heat sink for condensing the expanded working fluid from the turbine; and pumping means for pumping and pressurizing the condensed working fluid to the heat exchanger arrangement.
A normal or an Organic Rankine Cycle/process (ORC) gives up to now poor results as the working media normally vaporize at a constant (isothermal) temperature. Better results are obtained by non-isothermal conditions received normally by ammonia-water mixtures, as e.g. in the Kalina process. However, these require complicated process structures and some difficulties in selecting a suitable turbine/expander especially regarding its shaft speed.
The invention relates to an improved ORC of the type initially mentioned, in which the heat exchanger arrangement comprises at least three parallel coupled evaporators forming at least three pressure stages on the working fluid side, and providing one outlet per pressure stage for connecting to the at least one turbine.
Preferably, the at least one turbine is a single turbine including one inlet per pressure stage. Each inlet connected to respective pressure stage outlet. The turbine further having a common outlet for the expanded working fluid.
In some embodiments, the turbine may drive an electric generator. In other embodiments the turbine may e.g. drive a propeller axis, a compressor or a pump.
Preferably, the heat exchanger arrangement includes three evaporators, one for a low pressure stage, one for a medium pressure stage, and one for a high pressure stage, at least one economizer per pressure stage, and optionally at least one superheater per pressure stage.
Preferably, the heat exchanger arrangement includes: one economizer at the low pressure stage, two economizers at the medium pressure stage, and three economizers at the high pressure stage. The economizers at respective pressure stage being serial connected (if more than one) on the working fluid side.
Preferably, the heat exchanger arrangement is configured to heat the working fluid at each pressure stage to an individual temperature starting point at the corresponding turbine inlet, each starting point selected to be in the dry/superheated region. Preferably, the heat exchanger arrangement is configured such that each starting point is selected to provide the turbine expansion to end in within +_5° C. of a common temperature and pressure end point in the dry/superheated region. The common end point is preferably situated about 5-10% of the latent heat/enthalpy in the dry/superheated region of the saturation curve from the saturation curve. More preferably, the common end point is situated about 1-2% of the latent heat/enthalpy in the dry/superheated region of the saturation curve from the saturation curve.
Preferably, at least two of the evaporators are coupled in series on the heat source side, such that at least a portion of the heat source flow is directed through the evaporators in series. More, preferably at least three evaporators are coupled in series on the heat source side.
In one embodiment, the pressure stages are selected such that the vaporization temperatures of the evaporators are within T2+An*(T1−T2)+−15%, where An=(1/(n+1), 2/(n+1), . . . , (n)/(n+1)), where n being the number of evaporators, and where T1 being the temperature of the heat source and T2 the temperature of the heat sink. Preferably the variation is selected as +−10%.
A new turbine design matching the new heat arrangements is suggested. The turbine is of a turbo machine type, e.g. an impulse/action type or a reaction turbine and having at least two inlets, and directing means in the form of guiding vanes and/or nozzles for directing a flow from said inlets on to different radii of one common turbine wheel of the turbine.
The turbine may be a reaction turbine preferably of a radial or a mixed flow type with a centripetal (inwards) flow direction with a casing and at least one runner/wheel with working blades, at least two inlets and one common outlet where the inlets in turn are connectable to guiding vanes/nozzles in the turbine casing for expansion of the gas at different radii.
The turbine may alternatively be an impulse/action type with a disc that has blades at different radii to match the driving expanded flow from the nozzles whereby at least two sets of the nozzles are situated at different radii and the remaining at equal radii but at separate angular sectors. Preferably having at least two of the said guiding vanes/nozzles situated on different diameters D4 and D4′ respectively. Preferably, having the said runner working blades with an extension to at least two different diameters D2 and D2′ respectively.
The turbine/expander may be of a positive displacement machine type with several stages by having displacement volumes determined by a first actual flow stream of the working fluid to which part working fluid streams are further added between the stages and that the downstream displacement sizes are correspondingly increased to swallow the total vapor flows. Preferably, displacement machine is a screw expander/turbine with one or several screws designed to be a 2 or 3 stage machine with intermediate inlets for said part flow streams between the stages and that the downstream screw displacement/volume capacity is designed by selecting shape, size and/or the number of the “pistons” in a first/male and slots in a second/female rotor cooperating with the first to swallow both the actual and the total volume flows.
The invention will further down be presented in detail with reference to the drawings/figures in which:
A waste heat process using sensible heat has normally three different circuits; a heat source circuit 1, a working fluid circuit 2 and a heat sink 3,
The fluid of the heat source (gas or liquid) passes and exchanges heat, in a possible superheater 14, an evaporator 13 and an economizer 12 with a decrease in temperature from 1′ to 1″.
The working fluid in 2 passes said heat exchangers with a change in state from liquid to vapor with a corresponding increase of its energy content from 2 to 2″. In a turbine/expander 15 connected to an electric generator 159 the fluid expands and gives away energy.
The vapor of fluid 2 is led to a condenser 16 and from this to a possible tank 17 preferably placed below the condenser. A feed pump 11 closes the circuit by pumping the fluid into said heat exchangers.
The heat sink 3 cools the condenser and may have a pump 17. The heat sink may e.g. be ambient (cold) water or air or indirectly a liquid from a cooling tower or an air-cooled radiator.
A graph,
The heat source 1 is given by an approximately straight line, the working process 2 by a closed circuit 2 and the heat sink by the line 3. The said components are marked with equal figures as in
In the circuit 2 the evaporation is shown as the line 13, the economizer by 12 and the superheater by 14. The line 13 is shown oblique to the W-axis that means the liquid vaporizes at varying temperatures or at non-isothermal conditions (as in the Kalina process). This is typical for mixtures of different media. For a pure fluid or an azeotrophic mixture the line 13 is horizontal as it vaporizes at a constant temperature. Similar conditions are valid for the line 16 at the condenser.
An expansion of the working fluid is marked 15 and 151 of which 15 represents the useful mechanical work obtainable as input/output to/from the turbine. The size of this work is also given as the distance 0-150 while the total source heat flow is 0-1″.
The temperature profile as shown in
An inner or net part is defined by the line 2 and 16 with a temperature difference t1−t2. From the geometry it is obvious that these two are given solely by 14″, 12″ and 16′. The “knee” at 12″ is in English literature called “pinch point”. A net efficiency is obtained from t1 and t2 with the difference t.
For the said heat exchangers including the condenser, temperature differences are required to drive a heat transfer. In
A temperature heat flow part marked as 151 is the waste heat from the inner process 2. As the temperature is above that of the heat sink it can, known per se, be recovered by a recuperator and utilized for an improvement of the inner process shown in
Known, elementary and rather common is to use evaporation at 2 different temperatures (pressures) especially in combination with several heat sources with considerably different temperatures, e.g. 250 and up and 90 degree C. respectively. Some examples are shown below with a broad variation in ways to couple two sets of components together.
U.S. Pat. No. 6,857,268 B2, a cascade solution where a low pressure circuit is fed by vapor heated by expanded vapor from a high pressure circuit. Each circuit has a separate turbine. The solution is thermodynamically poor and is possibly selected due to turbine limitations.
U.S. Pat. No. 8,438,849 B2, has two heat sources with different temperatures/pressures, where in two alternatives vapor from a high pressure turbine in series with vapor from the other sources is fed to a low pressure turbine. In a third alternative the two heat sources are coupled in parallel to independent vaporizers and independent turbines and then to a common condenser. In a forth alternative the two heat sources have independent circuits including turbines and condensers with water as working fluid for one of the circuits.
U.S. Pat. No. 8,474,262 B2, has one heat source and two separated independent circuits complete with all components as well as turbines, where the split between the two circuits is optimized.
US 2010/0071368 A1, has an ORC with a cascade coupling where expanded vapor from the high pressure turbine is fed to the low pressure turbine and in an alternative parallel circuits each coupled to a turbine. In a further alternative there are two totally independent circuits of which one has water as working fluid.
US 2010/0242476 A1, this is similar to U.S. Pat. No. 6,857,268 B2 with a cascade solution for high and low pressures circuits.
US 2010/0242479 A1, similar to US 2010/0242476 A1, but with a back end for generation of heating/refrigeration added.
US 2014/0026574 A1, has 2 heat sources and sets of evaporators, screw expanders/turbines coupled in series. The screw expanders can have wet condition for the working fluid, which normally is avoided due to damage risk in normal turbines.
US 2014/0033711A1, has evaporation at different pressures/temperatures each coupled to two expanders/turbines of the screw type for wet service.
WO 2014/0211708 has several heat sources connected to separate evaporators, turbines in parallel for the heat source fluid as well as the working fluid. The circuits are connected to one common condenser.
The present invention ECT uses in contrast to the prior art a single heat source and multiple vaporization temperature/pressures. The flow pattern through the heat exchangers (evaporators) is parallel for the working fluid and series for the heat source fluid. The reason is to gain more electric output from the same heat source by matching the temperature profile of the heat source fluid with that for the working fluid. The tail of the heat source profile will then get a low outlet temperature close to that of the heat sink.
WO 2013/171685 A1 shows a “multistage” radial turbine design for adding/removal of a part fluid flow (intermediate superheating) with a pressure between the pressures and with adding/removal also between the normal in- and outlets. The main flow direction is centrifugal (outwards). The turbine design is similar to a Ljungström radial turbine but with one of the counter rotating part replaced by a stationary vane set.
DE 10 2012 021 357 A1 2014.05.08 shows an ORC with evaporation in two stages with heat taken from the heat source and then in a further stage with heat from a recuperator. The main vapor streams and part streams are fed into a multistage axial turbine between the turbine stages. In one of the claims the number of evaporation stages may be increased with the same principles that among other things mean that the said coupling of the heat exchangers remain and are equal.
CN 103195519 A shows an ORC with 4 evaporation stages coupled in series and driven by heat from the heat source and a further stage driven by heat from a recuperator. Vapor from the working fluid is schematically supplied to different parts of a turbine. If the working circuits are coupled in series as in this prior art separating means must be arranged between the stages as a pressure difference between liquid out from a preheater and into an evaporator due to obtain sufficient NPSH for avoiding cavitation in the pumps. Alternatively the separation could be done by a vapor/liquid tank/boiler or the pumps placed well below the exchangers. Another disadvantage is that separate pumps are necessary
ECT is an acronym for “Enthalpy Compounding Technology”. ECT is an invention with the intention to improve the economic conditions for generating electricity out from waste heat sources. Typical for these are that the heat is found in a sensible form that means that the temperature is gradually decreasing when heat is taken out.
The ECT may take advantage of the temperature profile for a sensible heat source in that a performance optimum is selected.
According to an embodiment, the performance optimum for a process with one single evaporation process below a temperature difference below 100° C. is an average vaporization temperature (e.g. a vertical mean of line 13 in
The total or gross efficiency/gain is first and foremost defined as the net output as mechanical work in relation to the available heat between the heat source max temperature down to the minimum temperature of the heat sink. A part efficiency is sometimes erroneously calculated for the working circuit itself that, however, cannot be used for any technical and/or economical consideration.
For a simple case with the heat source line 1 as a straight line together with several evaporation temperatures the optimum will get about the same average as stated above. The
In other embodiments, the ECT process may feature several different vaporization temperatures or pressure levels at which heat is transferred in the process, preferably as separate part flow circuits 2H, 2M and 2L,
All the vaporization temperatures are then optimized for max output/gain. By advantage a pure or an aezotrophic fluid is used with 3 different vaporization temperatures. In the general case at least one of the pressure level may be above the critical point (critical pressure) for the working fluid, a point above which no vaporization occurs at heating. One embodiment of the invention uses basically evaporation with at least 3 different temperatures/pressures, usually 3, at at least one heat source at a certain given max temperature.
In
The differences at the knees (pinch points), 12″, are further economically optimized with regard to obtained electrical output/gain and the cost of the heat exchangers. The differences at 12″ are the driving “force” for the heat transfer. Typical is here differences less than 5% of the temperature span 1′ to 1″ and with preferable values of 2-3%.
The overall aim with the invention is to use the heat source as well as possible, preferable down to the heat sink. In
In an embodiment using several pressure stages the optimal vaporization temperature may be selected to be within T2+An*(T1−T2)+−15%, where An=(1/(n+1), 2/(n+1), . . . , (n)/(n+1)), where n being the number of evaporators, and where T1 being the temperature of the heat source and T2 the temperature of the heat sink. Preferably the tolerance being +−10%. E.g. for a three stage system having a heat source temp of 100° C. and a heat sink temp of 20° C., the vaporization temperatures could be selected as (40° C., 60° C., 80° C.), the values with variation of +−15%, preferably +−10%.
By several sets of heat exchangers the fluids flowing through them must not be equally or symmetrically coupled. In general each heat exchanger has four connection ports for in/out for the two fluids exchanging heat, compare
ECT has according to the invention the part circuits for the working fluid high H, medium M and low L pressures in
For the economizers/preheaters 12 as an alternative, some of the pipelines can be common as shown by the alternative circuit in
As can be seen in
a, and 14 show alternative couplings of the heat exchanger arrangement 12-14 on the heat source side.
The heat source flow circuit,
In the alternative heat source circuits in
As can be seen in the embodiments of
Due to cost reduction ECT uses preferably a very small superheating of the vapor from the part evaporators normally with different values for all of them.
When the working fluid has a lower slope on its saturation curve than the isenthrops corrected for turbine losses a recuperator may be used. By the common point C123, energy losses are avoided as when fluids with different temperatures (enthalpies) are mixed.
When the saturation curve and the corrected isenthrops are about parallel, The point C123 is selected close to the saturation curve at the condensation temperature t2. The horizontal distance C123-C0 is then according to the invention preferably selected to 1-2% of the latent enthalpy and no more than 5-10%. The said superheating may be made directly in the evaporators and separately superheaters are not necessary. The endpoint from the vapor expansion C123 is so adjacent to the saturation curve that heat recovery (C123 to C0) in a recuperator not is necessary.
The graph
The multistage evaporations in ECT give different enthalpies for a turbine/expander. Efficiency for axial turbines as well as reaction turbines is basically related to a relation between a vapor/steam velocity c and a peripheral velocity u with a typical dependence as shown in
The new action turbine of the impulse type,
For the lowest guiding vane velocity c a separate blade passage may be placed at a smaller radius in the disc. For an ORC (Organic Rankine Cycle) this can be done as peripheral velocities u are considerably lower than for a water steam turbine and structural stresses correspondingly lower. Alternatively, a second turbine wheel could be used.
For low mass flow loaded wheels the three nozzle groups may be arranged at an equal wheel radius.
An ECT radial/mixed flow turbine,
Said runner is operable in a casing 56 with volute shaped parties a first 61, a second 62 and a third 63 placed at at least on another part of the circumference. They are connected to different inlets (not shown) from the ECT working fluid (process) circuits. In the casing a holder 64 equipped with guiding vanes sets a first one 65, a second one 66 and a third 67 are clamped by a cover 57 connected to the casing by screws 58. Said cover has an outlet opening with a connection flange 59.
The runner blades and the said cover has a relatively tight clearance as well as the radially extended distance between the runner wall 54 and the vane holder 64 in order to avoid mitigation of the turbine performance. The rotatable separation wall 54 may be replaced by said holder 64 extended radially inwards to meet the diameter D2′ and having a tight axial clearance to the blades 51.
The at least two ECT process circuits have different enthalpy drops that in turn at an expansion give different absolute velocities c. For the fluid design of the turbine with a peripheral velocity u and an absolute velocity c just outside the runner, a velocity ratio u/c should equal about one to obtain a high efficiency. The desired velocity ratio u/c is obtained by varying either u or c or even both of them simultaneously.
In the radial vaneless gaps, given by the diameter differences D4−D2 and D4′−D2′ respectively, the flow follows a free vortex law that has the feature; that radius times the tangential component of the absolute velocity cu is constant. A smaller radius in the gap then gives a higher velocity cu. Here the velocity c is about equal to cu. Then the desired ratio u/c is obtained by selecting the diameters D2, D2′ and/or D4, D4′ accordingly.
The general configuration may be varied in several ways known per se. The semi open runner in
The velocity ratios u/c are different for an axial impulse turbine (de Laval action type with 0% reaction) with u/c about 0.4-0.5 and a radial turbine with 50% reaction where u/c is equal to about one. For the radial turbine with 50% reaction c is about 70% of the value of c for an action turbine.
For a radial turbine the different radii may be arranged as a stepped outside wheel diameter with 3 steps (the
The basic principle of the ECT can be applied on other expander/turbine types as on the broad family of positive displacement machines. As an easily understandable example a triple (3 stages/cylinders in series) compound steam/vapor machine shall be mentioned. The adoption to ECT means that part working fluid streams are added between the stages and the cylinder sizes are adapted to the corresponding increased vapor flows.
The screw expander with 2 screws, developed from the Lysholm screw compressor, or a single screw expander with side mounted sealing wheels can also be designed as a 2 or 3 stage machine with intermediate inlets for adding part flow streams between the stages. The screw volume capacity is changed by selecting the size and/or the number of the “pistons” in the male and the slots in the female rotor/rotors according to the volume flow. Note, when these changes are arranged within common rotors, the screw pitch must be equal for all parts.
Converting heat to cost efficient electricity generated at:
By ECT the electric output/gain is more than doubled compared to conventional commercial ORC processes using the same heat source and the same heat sink. ECT compares also well with non-isothermal vaporization processes. In addition ECT has a simpler structure and better conditions for the turbine/expander.
The ECT improvement is based on a systematic thermodynamical analysis, first defining a theoretical process analogous with the Carnot process working between two constant temperatures and then applying the result to practical conditions regarding working fluid and process components.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1451108-3 | Sep 2014 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2015/050982 | 9/21/2015 | WO | 00 |
