The engine is the heart of a Power Conversion Subsystem (PCS) located at the focal point of a sun-tracking parabolic dish concentrator. The ORC engine employs a single-stage axial-flow turbine driving a high speed alternator to produce up to 25 kW electrical output at the focus of each dish. The organic working fluid is toluene, circulating in a closed-loop system at temperatures up to 400 C (750 F). Design parameters, system description, predicted performance and program status are described

Boda, F. P.

English

NASA Technical Reports Server

THE SCSE ORGANIC RANKINE DIGINE 
by 
I 
F'. P .  Boda 
FORD AEROSPACE & COMMUNICATIONS CORPORATION (FACC) 
NEWPORT BEACH, CALIFORNIA 9 2660 
ABSTRACT 
This paper d e s c r i b e s  the  Organic Rankine Cycle (ORC) engine c u r r e n t l y  u n d e ~  
development f o r  the  Small Conununity S o l a r  Thermal Power Experiment (SCSE) f o r  
JPL/DOE cnder Cont rac t  955637. This  engine i s  the  h e a r t  of a Power Conversion 
Subsystem (PCS) loca ted  a t  the  f o c a l  p o i n t  of  a sun- t racking pa rabo l i c  d i s h  
concen t ra to r .  The ORC engine employs a s i n g l e - s t a g e  ax ia l - f low t u r b i n e  d r i v -  
ii.; a  h igh speed a l t e r n a t o r  t o  produce up t o  25 kW e l e c t r i c a l  ou tpu t  a t  t h e  
focus of  each d i s h .  The c , m i c  working f l u i d  i s  to luene ,  c i r c u l a t i n g  i n  a 
c losed- loop system a t  temperature up t o  4 0 0 " ~  ( 7 5 0 " ~ ) .  
Design parameters,  system d e s c r i p t i o n ,  p red ic ted  performance and program 
s t a t u s  a r e  desc r ibed .  The f i r s t  SCSE Organic Rankine Power Conversion Sub- 
system w i l l  be d e l i v e r e d  t o  the  JPLIEdwards t e s t  s i t e  i n  May 1981. 
INTRODUCTION 
Under Phase I1 of t h e  SCSE Program, FACC w i l l  develop a s o l a r  thermal,  p o i n t  
focusing,  d i s t r i b u t e d  r e c e i v e r ,  d i s t r i b u t e d  genera t ion  system employing a 
small  Rankine-cycle power conversion subsystem (PCS) sounted a t  the  focus  of  
a p a r a b o l i c  d i s h  concen t ra to r .  This paper d e s c r i b e s  only  the  Rankine-cycle 
PCS. The o v e r a l l  system and the  s o l a r  r e c e i v e r  ( b o i l e r )  a r e  addressed i n  
companion papers by R .  Pons and H.  Haskins, r e s p e c t i v e l y .  
The PCS conver t s  the  thermal energy of superheated vapor from t h e  r e c e i v e r  
i n t o  s h a f t  horsepower which d r i v e s  a d i rec t -coup led  a l t e l  s t o r  a t  the  f o c a l  
po in t .  This  h igh frequency ac power i s  conver ted  t o  dc by a ground-mounted 
r e c t i f i e r ,  combined wi th  the  ou tpu t s  from o t h e r  d i s h e s ,  then i n v e r t e d  t o  60 Hz 
ac e l e c t r i c a l  power supp l i ed  d i r e c t l y  t o  t h e  u t i l i t y  g r i d .  
The Rankine c y c l e  was s e l e c t e d  f o r  the  SCSE program on t h e  b a s i s  of  h i g h e s t  
performance f o r  l e a s t  program r i s k  (compared wi th  o t h e r  hea t  engine c y c l e s ) .  
The o rgan ic  Rankine c y c l e  (ORC) engine was chosen over  a steam Rankine engine  
on the  b a s i s  of  programmatic and t e c h n i c a l  f a c t o r s .  FACC has  s e l e c t e d  Barber-  
Nichols Engineering Company (B-N) of Arvada, Colorado, t o  des ign  and b u i l d  
the PCY. B-N i s  c u r r e n t l y  i n  the  hardware f a b r i c a t i o n  phase and assembly of 
t h e  f i rs t  u n i t  is  scheduled f o r  completion nex t  month. 
https://ntrs.nasa.gov/search.jsp?R=19810021984 2020-03-21T09:48:19+00:00Z
SYSTEM DESCRIPTION 
The power conversion subsystem is comprised o f  a very  compact t u r b i n e - a l t e r -  
nator-pump assembly, an a i r -coo led  condenser,  a  r e g e n e r a t o r ,  boost  pump, 
s t a r t  pump, va r ious  va lves ,  plumbing and i n s t r u a m t a t i o n .  The PCS a l s o  i n -  
c ludes  c e r t a i n  ground-mounted e l e c t r i c a l  suppor t  equipment, such a s  t h e  
r e c t i f i e r ,  overspeed brake c o n t r o l l e r ,  r e l a y s ,  e t c .  
Figure  1  i s  a  cutaway view of  the  PCS c o n f i g u r a t i o n ,  shown a t t ached  t o  the  
FACC cavi ty- type r e c e i v e r  assembly. The c y l i n d r i c a l  condenser shape r e s u l t s  
i n  an e f f i c i e n t  PCS packaging arrangement about 1.1 m (44") d i a  x  1 .5  m 
(60") long. The power conversion assembly shown i n  Figure  1 is  designed t o  
a t t a c h  to  the  mounting r i n g s  of the  General  E l e c t r i c  Low Cost C m c e n t r a t o r  
(LCC) cind provide minimum shadowing of the  mi r ro r  s u r f a c e .  PCS weight a t  the  
foca l  po in t  is  about 322 Kg (710 l b s . ) .  
A cutaway view of the  t u r b i n e - a l t e r n a t o r  pump (TAP) assembly is  shown i n  
Figure  2 .  The TAP is  an extremely compact dev ice  -- about the  s i z e  of a  
f o o t b a l l .  I t  has one r o t a t i n g  s h a f t  wi th  the  t u r b i n e  wheel mounted a t  one 
end, t ! i L d  a l t e r n a t o r  r o t o r  i n  the  middle and t h e  feed pump impe l l e r  a t  the  
o t h e r  end. The s h a f t  s p i n s  on hydrodynamic f l u i d - f i l m  bear ings  fed  by 
toluene l u b r i c a n t  passages through the  s h a f t  i t s e l f  . S a l i e n t  f e a t u r e s  o f  
the TAP a r e  l i s t e d  below. 
TUREINE 
S ing le  s t a g e ,  a x i a l  flow 
ALTERNATOR 
Permanent magnet (PMA) type 
F u l l  admission, 10 nozzlcs  Rotor: 6  Samarium Cohalt  magnets 
Inconel 718, 110 blades  S t a t o r :  9 - too th ,  copper wound 
Tip diameter 125 mn (4.92") 7 2  mn (2.8") OD x 127 mn (5.0t ')1 
B!ade he igh t  10.7 mn (0.42") 3  0 ,  3000 Hz AC a t  60,000 rpm 
Turbine e f f i c i e n c y  75% 95.0% peak e f f i c i e n c y  
Turbine speed j s  nominally 60,000 rpm. I t  v a r i e s  over  a  narrow range 
(55,000 t o  60,000) a s  a  func t ion  of input lower. 60,000 rpm i s  not  an 
excess ive  speed f o r  turbomachinery (autumotivc turbochargers  run twice a s  
f a s t ) .  I t  i s  t h i s  r e l a t i v e l y  high opera t ing  speed which makes t h e  smal l  TAP 
hardware s i z e  p o s s i b l e .  As an example, the  SCSE a l t e r n a t o r  i s  about one-twen- 
t i e t h  the s i z e  and v e i g h t  of more convent ional  generators a s s o c i a t e d  wi th  r e -  
c ip roca t ing- type  h e a t  engines .  This t u r b i n e  speed a l s o  al lows thc  main feed 
pump t o  supply the  f u l l  system flow a t  p ressures  up t o  5.9 MPa (855 p s i )  wi th  
a c e n t r i f u g a l  impel ler  on ly  33 mn (1.3") i n  d iamete r .  
Thv condenser c o n s i s t s  o f  369 finned aluminum tubes i n  p a r a l l e l ,  a r ranged 
in  t h r e e  concen t r i c  l a y e r s .  Cooling a i r  is  drawn i n  a x i a l l y  by the  two-speed 
fan and exhausted r a d i a l l y  outward ac ross  the condenser tubes .  This d i r e c t i m  
of a i r  flow prevents  s t a l l i n g  of t h e  fan  motor dur ing  high winds. 
The regenerator  i s  simply a  hea t  exchanger desigrlcd t o  recover waste h e a t  
energy from the  t u r b i n e  exhaust  vapor and use i t  t o  pre-heat  the  l i q u i d  
before  i t  e n t e r s  the rece ive r  ( b o i l e r ) ,  thereby enhancing o v e r a l l  system 
e f f i c i e n c y .  The regenera to r  core  i s  cons t ruc ted  of s t a i n l e s s  s t e e l  tubing 
wi th  aluminum f i n s .  The l i q u i d  fo l lows one continuous path ( i n  the  counterf low 
d i r e c t i o n )  through t h e  f inned tubing which makes 112 p a s : %  through the  h o t  
vapor flow. 
The PCS is designed t o  o p e r a t e  a t  a l l  s o l a r - r e l a t e d  e l e v a t i o n  angles  from 
5" t o  90' above the  h o r i z o t .  For t h i s  reason,  the  hotwel l  ( l i q u i d  c o l l e c t i o n  
r e s e r v o i r )  i s  loca ted  a t  t h e  low po in t  of t h e  PCS. The t o t a l  working f l u i d  
inventory is  about 15 l i t res  (4  g a l ) .  The log p ressure  s i d e  of t h e  system 
opera tes  a t  sub-atmospheric p ressure  t o  opt imize  t u r b i n e  performance, so a 
small  e l e c t r i c a l l y - d r i v e n  c e n t r i f u g a l  boost  pump i s  used t o  provide a moder- 
a t e  p o s i t i v e  pressure  t o  feed l i q u i d  t o  the  main pump and t h e  bear ings .  The 
boost  pump ob ta ins  l i q u i d  from the hotwel l .  
The temperature of t h e  vapor a t  t h e  e x i t  o f  the  s o l a r  r e c e i v e r  i s  maintained 
near a cons tan t  3 9 9 " ~  ( 7 5 0 " ~ )  by means of a vapor t h r o t t l i n g  c o n t r o l  va lve  
between t h e  rece iver  o u t l e t  and t h e  t u r b i n e  i n l e t .  The cons tan t  temperature 
can be maintamed by c o n t r o l l i n g  t h e  mass flow r a t e  of the  %orking f l u i d  t o  
compensate f o r  v a r i a t i o n s  i n  s o l a r  f l u x  . v e l .  The vapor c o n t r o l  va lve  i s  a 
p in t l e - typc  valve operated by a hydraul ic  a c t u a t o r  which i s  powered by high 
p ressure  working f l u i d .  Valve command s i g n a l s  a r e  keyed t o  temperature sen- 
s o r s  a t  the  rece iver  o u t l e t .  
Figure  3 i s  a s impl i f i ed  schematic diagram of t h e  PCS showing the  major com- 
ponents and t h e  plumbing loop. The Remote Control  I n t e r f a c e  Assembly (RCIA) 
box shown i n  the  f i g u r e  i s  a FACC-designed control ler /computer  loca ted  near  
t h e  base of each d i s h .  Each RCZA comunica tes  wi th  a Master Power C o n t r o l l e r  
(MPC) which performs c e n t r a l  c o n t r o l  and monitoring func t ions  For a l a r g e  
array of SCSE power modules. 
The organic  working f l u i d  i s  reagent grade to luene (C H CH ), a c l e a r  l i q u i d  
s i m i l a r  t o  comnon p a i n t  th inner .  The thermodynamic proper 6 5  ? i e s  of to luene a r e  
i d e a l l y  s u i t e d  f o r  use i n  small  ORC tu rb ines  f o r  s o l a r  a p p l i c a t i o n s .  Z t  
y i e l d s  high performance a t  . e l a t i v e l y  lower temperatures and p ressures ,  com- 
pared to  steam, and i ts  f reez ing  point  i s  minus 9 5 ' ~  (minus 139'). Toluene 
i s  a f u l l y  charac te r ized  scbstance and i t s  t o x i c i t y ,  f l amnabi l i ty  and o t h e r  
environmentally s e n s i t i v e  parameters a r e  q u i t e  we l l  known and s a f e  handl ing 
procedures a r e  w e l l  e s t a b l i s h e d .  
For any given working f l u i d ,  e f f i c i e n c y  inc reases  wi th  temperature;  however, 
a l l  organic f l u i d s  have an  upper temperature l i m i t  beyond which they tend 
t o  decompose, evolve noncondensfble gases ,  e t c .  Some e x i s t i n g  to luene 
systems have operated a t  4 2 7 " ~  ( 8 0 0 " ~ )  and beyond, but 3 9 9 " ~  (750°F) i s  
planned as the upper l i m i t  f o r  SCSE t o  promate lung f l u i d  l i f e  ( y e a r s ) .  The 
maximum temperature m a y  be ad jus ted  up o r  down a s  more experience i s  gained 
with the system. Adding 2 8 ' ~  (50°F) is  worth about 1% ga in  i n  o v e r a l l  sub- 
system cff  ic iency.  
A few ORC systems in  the  f i e l d  have experienced problems r e l a t e d  t o  leakage,  
i . e . ,  f l u i d  drgr \da t ion  caused by a i r ,  moisture o r  o i l  contaminating the 
working f l u i d .  For t h i s  reason,  t h e  SCSE system was designed a s  a h e r n e t i -  
c a l l y  sea led ,  closed-loop system t o  avoid t h e  p o s s i b l e  p i t  f a l l s  a ssoc ia ted  
wi th  high speed s h a f t  s e a l s .  Gearboxes, p ipe  th reads ,  r u s t ,  e t r .  The PCS 
t a s  no ex te rna l  moving s e a l s .  The toluene a c t s  t o  l u b r i c a t e  a l l  bear ings .  
V*WVI  ThllOTTLE VALVE 
RECEIVER CORE 
RLCt VER OUTER SMELL 
APERTURE PI ATE REGENERATOR 
START PUMP 
CORE 
FIGURE 1. POWER CONVERSION ASSEMBLY 
SUPERMLA~LD HIGHPRESS 
TOLUENE Lli UID TOLUENE 
OUT 
* E E D W  
F IGURE 2 .  TURB INE -ALTERNATOR. i iJMP ( TAP) F IGURE 3 .  POWER CONVERSION SUPSYSTEM 
(PCA) SCHEMATIC 
cool  t h e  a l t e r n a t o r  and pumps, and t o  o p e r a t e  t h e  hydrau l i c  a c t u a t o r  of t h e  
c o n t r o l  va lve  ( i n  a d d i t i o n  t o  i t s  primary func t ion  o f  powering t h e  t u r b i n e ) .  
E l e c t r i c a l  power o u t p u t  of  the  PCS is about 20 kW a t  r a t e d  cond i t ions  of  
75.6 kW thermal inpu t  and 2 6 3 ~  ( 8 2 " ~ )  ambient ai: temperature.  PCS outpu t  
is  abouk 25 kW a t  peak power c o n d i t i o n s  of 92.4 kW inpu t .  
e  t 
Figure  4 shows PCS e f f i c i e n c y  a s  a  f u n c t i o n  of  thermal inpu t  f o r  v a r i o u s  
ambient temperatures .  PCS e f f i c i e n c y  is def iced  a s  t h e  net dc e l e c t r i c a l  
power o u t  (account ing f o r  p a r a s i t i c s )  d ivided by thermal energy inpu t  from 
t h e  r e c e i v e r .  P red ic ted  e f f i c i e n c y  a t  r a t e d  power is  about 26 pe rcen t .  Note 
the  r e l a t i v e l y  £ l a c  shape of the  curves ,  denot ing high e f f i c i e n c i e s  a c r o s s  
a  very  broad range of s o l a r  o p e r a t i n g  cond i t ions .  This  e x c e l l e n t  "part- load" 
c h a r a c t e r i s t i c  he lps  maximize power o u t p u t  on an annual ized b a s i s  and n o t  j u s t  
a t  a r a t e d  power po in t .  
P R O G M .  STATUS 
Somc PCS components a r e  c u r r e n t l y  undergoing development t e s t i n g  a t  Barber- 
Nichcls .  B-N expects  to  complete assembly of the  f i r s t  d e l i v e r a b l e  u n i t  i n  
February,  t e s t  i t  a s  a  subsystem i n  March, t e s t  i t  combined wi th  the  FACC 
r e c e i v e r  and c o n t r o l l e r  i n  Apr i l  a d  s h i p  i t  to  the  JPL t e s t  s i t e  i n  May of 
CYCLE EFFICIENCY VSPOWER I N  -18Oc (oOF) 
AND AMPiiENT TEMPERATURE 10°C (50°F) 
2 8 ' ~  ( 8 2 O ~ )  
T 
I 4 9 O ~  ( 1  20°F) 
I 
I 
I 
I 
I 
RAT ED 
POWER 
POINT 
I 
I 
hlAX CYCLE T E M P  = 3 9 9 ' ~  ( 7 5 0 ' ~ )  
I 
. BOILER EXIT PRESS = 4 .48  MPa (650 p d i a )  
I 
I I I 
10 m 00 70 
u 
0 a0 90 100 
FIGURE 4 .  PCA PERFORMANCE 


The SCSE Organic Rankine engine

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server