The trilateral flash cycle system is a proposed means of power recovery from single-phase low-grade heat sources. Its feasibility depends on the efficient adiabatic expansion of light hydrocarbons from the saturated liquid phase into the two-phase region. Such a process is performed most effectively with a Lysholm twin-screw expander when the exhausted vapour is wet. At higher temperatures, when multi-stage expansion is required, working fluids may be found which complete the process as dry saturated vapour. It is shown that at condensing temperatures of 0–50°C, this is possible with a mixture of n-pentane and 2,2–dimethylpropane (neopentane) for fluid inlet temperatures in the 150–180 °C range. A radial inflow turbine may then be used in place of a screw for the last stage. With such an arrangement, expander adiabatic efficiencies of up to 85 per cent have been predicted for power outputs in excess of 5 MW. The method of fluid property estimation is described and its accuracy confirmed by experiment.
Get full access to this article
View all access options for this article.
References
1.
SmithI. K.Development of the trilateral flash cycle system. Part 1: fundamental considerations. Proc. Instn Mech. Engrs, Part A, 1993, 207(A3), 179–194.
2.
ElliottD. G.Theory and tests of two-phase turbines. JPL publication 81–105, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 15 March 1982.
3.
AmendW. E.TonerS. J.Power production with two-phase expansion through vapor dome. US Pat. 4 463 567, 7 August 1984.
4.
SwearingenJ. S.SchulzR. G.Flashing liquid runs turboexpander. Oil and Gas J., 1976, 74(27), 70–71.
5.
Vapour turbine performance and price quotation, Rotoflow Corporation, Los Angeles, California, 1987 (personal communication).
6.
Hot dry rock trilateral wet vapour cycle study contractor report, ETSU G 141, UK Department of Energy, 1988.
7.
SteidelR. F.WeissH.FlowerJ. E.Characteristics of the Lysholm engine as tested for geothermal applications in the Imperial Valley. J. Engng for Power, January 1982, 104, 231–240.
8.
TaniguchiH.KudoK.GiedtW. H.ParkI.KumazawaS.Analytical and experimental investigation of two-phase flow screw expanders for power generation. Trans. ASME, J. Engng for Gas Turbines and Power, 1988, 110, 628–635.
9.
TaborH.BronickiL.Establishing criteria for fluids for small vapour turbines. SAE Trans., 1965, 73, 561–575.
10.
SmithI. K.THERPROP—a computer program and subprogram set with data bank for volatile fluid thermal property estimation. City University, London, March 1984.
11.
SmithI. K.The use of the Lee–Kesler equations of state for the estimation of common refrigerant properties. Proceedings of NPL Conference on Chemical thermodynamic data on fluids and fluid mixtures, September 1978 (NPL, Teddington, Middlesex).
12.
StarlingK. E.KwokY.Thermo data for LPG. I. Equation of state and computer prediction. Hydrocarbon Processing, 1971, 50 (3), 101.
BenedictM.WebbG. B.RubinL. C.An empirical equation for thermodynamic properties of light hydrocarbons and their mixtures. I. Methane, ethane, propane and butane. J. Chem. Phys., 1940, 8, 334–345.
15.
BenedictM.WebbG. B.RubinL. C.An empirical equation for thermodynamic properties of light hydrocarbons and their mixtures. II. Mixtures of methane, ethane, propane and n-butane. J. Chem. Phys., 1942, 10, 747–758.
16.
BenedictM.WebbG. B.RubinL. C.An empirical equation for thermodynamic properties of light hydrocarbons and their mixtures. Fugacities and liquid–vapour equilibria. Chem. Engng Prog., 1951, 47(8), 419–422; 47(9), 449–454, 571–578 and 609–620.
17.
LeeB. I.KeslerM. G.A generalised thermodynamic correlation based on Pitzer's three parameter corresponding states principle. Ass. Ind. Chem. Engrs J., May 1975, 21(3), 510–527.
18.
PlöckerU.KnappH.PrausnitzJ. M.Calculation of high-pressure vapor-liquid equilibria from a corresponding-states-correlation with emphasis on asymmetric mixtures. Ind. Engng Chem. Process Des. Div., 1978, 17(3), 324–332.
19.
SoaveG.Equilibrium constants from a modified Redlich–Kwong equation of state. Chem. Engng Sci., 1972, 27(6), 1197–1203.
20.
RedlichO.KwongJ. N. S.On the thermodynamics of solutions. V. An equation of state. Fugacities of gaseous solutions. Chem. Rev., 1949, 44, 233–244.
21.
Pitanga Marques da SilvaR.Organic fluid mixtures as working fluids for the trilateral flash cycle system. PhD thesis, City University, London, May 1989.
22.
GraboskiM. S.DaubertT. E.Modified Soave equation of state for phase equilibrium calculations. Ind. Engng Chem. Process Des. Div., 1979, 18(2), 300–306.
23.
PitzerK. S.LippmannD. Z.CurlR. F.JrHugginsC. M.PetersenD. E.The volumetric and thermodynamic properties of fluids. I. Theoretical basis and virial coefficients. J. Am. Chem. Soc., 1955, 77(13), 3427–3432.
24.
PitzerK. S.LippmannD. Z.CurlR. F.JrHugginsC. M.PetersenD. E.The volumetric and thermodynamic properties of fluids. II. Compressibility factor, vapor pressure and entropy of vaporisation. J. Am. Chem. Soc., 1955, 77(13), 3433–3440.
25.
PitzerK. S.CurlR. F.JrThe volumetric and thermodynamic properties of fluids. III. Empirical equation for the second virial coefficient. J. Am. Chem. Soc., 1957, 79, 2369.
26.
WalasS. M.Phase equilibria in chemical engineering, 1985 (Butterworths, Stoneham, Mass.).
27.
PolingB. E.GrensE. A.PrausnitzJ. M.Thermodynamic properties from a cubic equation of state—avoiding trivial roots and spurious derivatives. Ind. Engng Chem. Process Des. Div., 1981, 20(1), 127–130.
28.
GundersenT.Numerical aspects of the implementation of cubic equations of state in flash calculation routines. Comput. Chem. Engng, 1982, 6(3), 245–255.
29.
ZiervogelR. G.PolingB. E.A simple method for constructing phase envelopes for multicomponent mixtures. Fluid Phase Equilibria, 1983, 11(2), 127–135.
