Design methodology for a small solar steam generation system using the flash boiler concept

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Energy Convers.Mgmt Vol. 37, No. I, pp. 1-15. 1996 Copyright © 1995ElsevierScienceLtd 0196-8904(95)00022-4 Printed in Great Britain.All rights reserved 0196-8904/95 $9.50+0.00

DESIGN METHODOLOGY FOR A SMALL SOLAR STEAM GENERATION SYSTEM USING THE FLASH BOILER CONCEPT
A. T H O M A S Karunya Institute of Technology, Karunya Nagar, Coimbatore 641 114, India

(Received 17 December1994; receivedfor publication 8 February 1995)

Abstract A solar steam generation system which generates steam around 250 kg/h is very useful for small and medium scale industries. Simple design methodologies for sizing various subsystems are presented in this paper. Parabolic trough concentrators trollers Flash boiler concept Flux line tracker Field and local con-

NOMENCLATURE hs = Specificenthalpy of saturated vapour (kcal/kg) hf = Specific enthalpy of saturated liquid (kcal/kg) hfl = Specific enthalpy at inlet temperature of water (kcal/kg) hfa = Specific enthalpy of water at Ps (kcal/kg) hga = Specific enthalpy of steam at Ps (kcal/kg) L = Latent heat (kcal/kg) x = Dryness fraction Qs = Heat required to produce I kg of steam QT = Total heat required to produce (250 × 8 = 2000 kg)of steam QR = Heat collected in each row of collector (kcal) T~w= Temperature of saturated water at inlet pressure of P (°C) Tsc = Subcooling (°C) T, = Ambient temperature (°C) Tw = Working temperature of collector field (°C) T~= Initial temperature of cold water (°C) Ts = Steam temperature (°C) AT = Total collector area (m2) AT/N = Area of collector in each row (m2) Aa = Aperture area of eachcollector (m2) mw = Mass flow rate of water at inlet (kg/h) ms = Steam generation (kg/h) Cp= Specific heat (keal/kg°C) Ps = Steam pressure (kg/cm 2g) Pw = Working pressure of collector field (kg/cm 2) P~ = Pressure of water from collector field at inlet to flash boiler [kcal/m 2 (a)] ID~= Daily average direct solar radiation (W/m2) r/c = Efficiency of collector module

INTRODUCTION T h e t e c h ni c a l a n d e c o n o m i c feasibility o f u s i n g solar e n e r g y to g e n e r a t e low p r e s s u r e s t e a m a r o u n d 150°C for i n d u s t r i a l processes has been d e m o n s t r a t e d by the U.S. D e p a r t m e n t o f E n e r g y b y i n s t a l l i n g 14 p l a n t s u s i n g p a r a b o l i c t r o u g h c o n c e n t r a t o r s ( P T C s ) [ 1 ] . Similarly, Italy, Po r t u g a l , G e r m a n y , Israel a n d J a p a n have installed as m a n y as seven systems e m p l o y i n g P T C s [2]. E i t h e r the flash b o i l e r c o n c e p t o r the u n f i r e d boiler c o n c e p t is used in these systems to g e n e r a t e steam. T h e solar s t e a m g e n e r a t i o n p l a n t installed at J o h n s o n a n d J o h n s o n , S h e r m a n , Texas,which is b a s e d o n the flash b o i l e r c o n c e p t is in o p e r a t i o n since the year 1980 [3]. Similarly, the solar s t e a m g e n e r a t i o n p l a n t i n s t a l l e d at the G o v e r n m e n t Silk F a c t o r y , M y s o r e , in 1987, the first o f its k i n d in I n d i a , is also b a s e d o n the flash b o i l e r c o n c e p t [4]. T h i s p a p e r discusses a s i m p l em e t h o d o l o g y

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THOMAS: A SMALL SOLAR STEAM GENERATION SYSTEM

to design a solar steam generation system, based on the flash boiler concept, having a generation capacity around 250 kg/h. FLASH BOILER SYSTEM In general, the solar flash boiler system consists of a collector field (consisting of parabolic trough concentrators), flash boiler, circulating and feed pumps,instrumentation and controls. As shown in Fig. 1, water from the flash boiler is pressurized and circulated through the collector field and heated to a temperature between 180 and 200°C. To prevent boiling within the collectors or the collector field piping, the water is pressurized and maintained at the required pressure by a circulating pump. The flash boiler is provided with a flash chamber. When the...
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