A multistage evaporation organic rankine cycle

Abstract

The invention ECT relates to methods for improving the amount of electricity gained from preferably waste heat by a normal or an organic (ORC) Rankine process with vaporization in several stages, normally three. The waste heat in sensible form is exchanged in at least two in series coupled evaporators to a receiving working fluid (e.g. a refrigerant) that passes at least two of said evaporators, but coupled in parallel. Of the waste heat between the temperature of the heat source and that of the heat sink about 80% can be used for direct electricity generation. An embodiment of the invention uses a radial turbine with a centripetal (inwards) flow direction. The different vapor enthalpies from the said vaporization stages enters a turbine wheel/runner 51 at different outside diameters D2, D2′ and/or with suitable tangential velocities obtained by different guiding vane sets 65, 66 and 67.

1 . An apparatus of Organic Rankine Cycle type including a closed loop working fluid circuit ( 2 ) operable between a heat source ( 1 ) and a heat sink ( 3 ), the working fluid circuit including:
 a heat exchanger arrangement ( 12 - 14 ) for vaporizing and/or superheating a working fluid by exchanging energy from the heat source ( 1 );   at least one turbine ( 15 ) for expanding the vaporized/superheated working fluid;   condensing means ( 16 ) connectable to the heat sink ( 3 ) for condensing the expanded working fluid from the turbine; and   pumping means ( 11 ) for pumping and pressurizing the condensed working fluid to the heat exchanger arrangement ( 12 - 14 );   wherein the heat exchanger arrangement ( 12 - 14 ) comprising at least three parallel coupled evaporators forming at least three pressure stages (L, M, H) on the working fluid side, and providing one outlet per pressure stage for connecting to the at least one turbine ( 15 ).   
     
     
         2 . The apparatus according to  claim 1 , wherein the at least one turbine ( 15 ) is a single turbine ( 15 ), said turbine including one inlet per pressure stage connecting to respective pressure stage outlet, and a common outlet ( 59 ) for the expanded working fluid. 
     
     
         3 . The apparatus  claim 1 , wherein the heat exchanger arrangement includes:
 three evaporators, one for a low pressure stage ( 13 L), one for a medium pressure stage ( 13 M), and one for a high pressure stage ( 13 H);   at least one economizer ( 12 L,  12 M,  12 H) per pressure stage; and optionally at least one superheater ( 14 L,  14 M,  14 H) per pressure stage.   
     
     
         4 . The apparatus  claim 1 , wherein the heat exchanger arrangement includes: one economizer ( 12 L) at the low pressure stage, two economizers ( 12 M′,  12 M) at the medium pressure stage, and three economizers ( 12 H″,  12 H′,  12 H) at the high pressure stage. 
     
     
         5 . The apparatus  claim 1 , wherein the heat exchanger arrangement ( 12 - 14 ) is configured to heat the working fluid at each pressure stage (L, M, H) to an individual temperature starting point (S I, S 2 , S 3 ) at the corresponding turbine inlet, each starting point (S I, S 2 , S 3 ) selected to be in the dry/superheated region. 
     
     
         6 . The apparatus according to  claim 5 , wherein the heat exchanger arrangement ( 12 - 14 ) is configured such that each starting point (S I, S 2 , S 3 ) is selected to provide the turbine expansion to end in within +/−5° C. of a common temperature and pressure end point (CI  23 ) in the dry/superheated region. 
     
     
         7 . The apparatus according to  claim 6 , wherein the common end point (C 123 ) is situated about 5-10% of the latent heat/enthalpy (CO to COO) in the dry/superheated region of the saturation curve from the saturation curve. 
     
     
         8 . The apparatus according to  claim 7 , wherein the common end point (C 123 ) is situated about 1-2% of the latent heat/enthalpy (CO to COO) in the dry/superheated region of the saturation curve from the saturation curve. 
     
     
         9 . The apparatus  claim 1 , wherein at least two of the evaporators ( 13 L,  13 M,  13 H) 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 ( 13 L,  13 M,  13 H) in series. 
     
     
         10 . The apparatus  claim 1 , wherein the pressure stages are selected such that the vaporization temperatures of the evaporators are within T 2 +An*(Tl−T 2 )+/−15%, where An=(l/(n+l), 2/(n+l), . . . , (n)/(n+l)), where n being the number of evaporators, and where Tl being the temperature of the heat source and T 2  the temperature of the heat sink. 
     
     
         11 . The apparatus according to  claim 2 , wherein the turbine ( 15 ) is of a turbo machine type being an impulse/action type or a reaction turbine and having at least three inlets, and guiding vanes and/or nozzles ( 65 ,  66 ,  67 ) for directing a flow from said inlets on to different radii of one common turbine wheel ( 52 ) of the turbine. 
     
     
         12 . The apparatus according to  claim 11 , wherein the turbine is a reaction turbine of a radial or a mixed flow type with a centripetal (inwards) flow direction with a casing ( 56 ) and at least one runner/wheel ( 50 ) with working blades ( 51 ), at least three inlets and one common outlet ( 59 ) where the inlets in turn are connectable to guiding vanes and/or nozzles ( 65 ,  66 ,  67 ) in the turbine casing for expansion of the gas at different radii. 
     
     
         13 . The apparatus according to  claim 11 , wherein the turbine is an impulse/action type with a disc ( 52 ) that has blades ( 51 ) at different radii to match the driving expanded flow from the guiding vanes and/or nozzles ( 65 ,  66  and  67 ) whereby at least two sets of the vanes/nozzles are situated at different radii and the remaining at equal radii but at separate angular sectors. 
     
     
         14 . The apparatus according to  claim 12 , wherein having at least two of the said guiding vanes and/or nozzles situated on different diameters D 4  and D 4 ′ respectively. 
     
     
         15 . The apparatus according to  claim 14 , wherein having the said runner working blades with an extension to at least two different diameters D 2  and D 2 ′ respectively. 
     
     
         16 . The apparatus according to  claim 1 , wherein the turbine is 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. 
     
     
         17 . The apparatus according to  claim 16 , wherein the displacement machine includes 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.