The viability of using fluidized bed heat exchangers (FBHX) for thermal energy storage (TES) in applications with potential for waste heat recovery was investigated. Of the candidate applications screened, cement plant rotary kilns and steel plant electric arc furnaces were identified, via the chosen selection criteria, as having the best potential for successful use of FBHX/TES system. A computer model of the FBHX/TES systems was developed and the technical feasibility of the two selected applications was verified. Economic and tradeoff evaluations in progress for final optimization of the systems and selection of the most promising system for further concept validation are described

Ananth, K. P.

Ramanathan, V.

Weast, T. E.

English

NASA Technical Reports Server

THERMAL ENERGY STORAGE SYSTEMS USING 
FLUIDIZED BED HEAT EXCHANaRS* 
V. Ramanathan,' T. E .  Weast, and K. P. Ananth 
Midwest ~ e i e a r c h  ~ n s t i t u t e  - Kansas C i t y  
SUMMARY 
A systems s tudy i s  being conducted t o  determine t h e  v i a b i l i t y  of 
u s ing  F lu id i zed  Bed Heat Exchangers (FBHX) f o r  Thermal Energy Storage  (TES) 
i n  a p p l i c a t i o n s  w i t h  p o t e n t i a l  f o r  waste h e a t  recovery.  Of the  candida te  
a p p l i c a t i o n s  screened,  Cement P l an t  Rotary Ki lns  and S t e e l  P l a n t  E l e c t r i c  Arc 
Furnaces were i d e n t i f i e d ,  v i a  t he  chosen s e l e c t i o n  c r i t e r i a ,  a s  having the  b e s t  
p o t e n t i a l  f o r  succes s fu l  use of FBHX/TES system. A computer model of t he  FBHX/ 
TES systems has been developed and the t e c h n i c a l  f e a s i b i l i t y  o f  t he  two s e l e c t e d  
a p p l i c a t i o n s  has been v e r i f i e d .  Economic and t r ade -o f f  eva lua t ions  a r e  i n  pro- 
g r e s s  f o r  f i n a l  op t imiza t ion  of the  systems and s e l e c t i o n  of  t he  most promising 
sys  tem f o r  f u r t h e r  concept v a l i d a t i o n .  
INTRODUCTION 
The development of e f f i c i e n t  (TES) systems i s  necessary  f o r  many 
energy conserva t ion  programs t o  be t e c h n i c a l l y  and economically a t t r a c t i v e .  By 
u t i l i z i n g  the mass o f  a  f l u i d i z e d  m a t e r i a l  f o r  thermal energy s to rage ,  the  
energy t r a n s f e r  and s to rage  func t ions  can be i n t e g r a t e d  i n t o  a  common FBHX/TES 
system. Systems used f o r  recovery of  s e n s i b l e  h e a t  gene ra l ly  use  e i t h e r  con- 
veh t iona l  t ubu la r  type exchangers o r  d i r e c t  con tac t  o f  a  working f l u i d  wi th  a  
f i xed  s to rage  media which r e q u i r e  la rgeqhea t  t r a n s f e r  s u r f a c e  a reas  and may be 
s u b j e c t  t o  plugging of t h e  flow by loose p a r t i c l e s .  I n  a d d i t i o n  t o  TES, FBHX's 
can e l imina te  these  p o t e n t i a l  h e a t  t r a n s f e r  problems. 
The o b j e c t i v e  of t h i s  p r o j e c t  i s  t o  i d e n t i f y  and ana lyze  ope ra t ing  
c h a r a c t e r i s t i c s  and economics of p o t e n t i a l  FBHX/TES systems when used f o r  waste 
h e a t  recovery and u t i l i z a t i o n .  The conceptual  s tudy  formulated t o  address  t h i s  
o b j e c t i v e  i s  d iv ided  i n t o  two major tasks .  Task I d e f i n e s  p o t e n t i a l  FBHX con- 
cep t s  and i d e n t i f i e s  p o t e n t i a l  a p p l i c a t i o n s  i n t o  which 'IXS can be e f f i c i e n t l y  
i n t eg ra t ed .  Task I1 eva lua t e s  the  t echn ica l  and economic f e a s i b i l i t y  of  the  two 
* NASA - Lewis Research Center;  Cont rac t  No. DEN 3-96. 
https://ntrs.nasa.gov/search.jsp?R=19800014304 2020-03-21T17:59:37+00:00Z
most promising systems i d e n t i f i e d  i n  Task I and recommends one a p p l i c a t i o n  f o r  
a d d i t i o n a l  s tudy o r  demonstration. 
This  paper suuunarizes t h e  r e s u l t s  of Task I and the  s t a t u s  of  Task 
I1 which i s  s t i l l  i n  progress .  In t e r im  conclusions and f u t u r e  e f f o r t s  a r e  
a l s o  presented.  
TASK I - FBHX CONCEPT DEFINITION, TES APPLICATION IDENTIFICATION, 
AND SYSTEM INTEGRATION AND SELECTION 
FBHX Concept Def in i t i on  
Since t h e  TES media is  the  mass o f  t he  FBHX bed m a t e r i a l ,  i t  i s  
necessary t o  eva lua t e  the numerous FBHX conf igu ra t ions  f o r  i d e n t i f i c a t i o n , o f  
t he  most e f f e c t i v e  types f o r  TES systems. Numerous conf igu ra t ions  of f l u i d -  
ized  bed hea t  exchangers a r e  poss ib l e .  Representa t ive  FBHX conf igu ra t ions  a r e  
depic ted  i n  F igure  1. A v e r t i c a l  mu l t i s t age  bed wi th  countercur ren t  con tac t -  
i ng  i s  presented i n  F igure  l ( a ) .  I n  t h i s  system, s o l i d s  a r e  heated by t h e  gas 
s t ream which i s  used t o  f l u i d i z e  the  bed. A f l u i d i z e d  bed wi th  an i n t e r n a l  
h e a t  exchanger i s  dep ic t ed  i n  F igure  l ( b ) .  The h igh  temperature i n l e t  gas 
f l u i d i z e s  the bed i n  t h i s  system. Crosscur ren t  con tac t ing  i n  a  mu l t i s t age  bed 
i s  shown i n  F igure  l ( c ) .  Heat exchange i s  between the  ho t  f l u i d i z i n g  gas and 
t h e  bed s o l i d s .  F igure  l ( d )  i s  a  cross-f low system wi th  an i n t e r n a l  h e a t  ex- 
changer, i n  which a i r  f l u i d i z e s  the  incoming ho t  alumina p a r t i c l e s  and h e a t  i s  
t r a n s f e r r e d  t o  the coo l ing  water c i r c u l a t i n g  i n  t he  h e a t  exchanger. F igures  
l ( e )  and I ( £ )  i l l u s t r a t e  l i q u i d  f l u i d i z e d  bed h e a t  exchangers wi th  i n t e r n a l  
h e a t  exchangers. 
The var ious  p o t e n t i a l  f l u i d i z e d  bed h e a t  exchanger/s torage conf ig-  
u r a t i o n s  were ranked according t o  such ope ra t ing  parameters a s  e f f i c i e n c y  of 
h e a t  recovery,  h e a t  t r a n s f e r  r a t e ,  system pressure  drop, environmental '  prob- 
lems, s t a b i l i t y  of  bed ope ra t ion ,  e t c .  The fo l lowing  conclusions were reached 
regard ing  the  a p p l i c a t i o n  of  f l u i d i z e d  beds f o r  energy s to rage :  
F lu id i zed  beds gene ra l ly  r e q u i r e  a  h igh  p re s su re  drop and hence, 
t h e i r  ope ra t ing  power requirements a r e  high.  This limits t h e i r  use t o  r a t h e r  
h igh  temperature a p p l i c a t i o n s  where the  amount of energy recovered i s  l a r g e  
r e l a t i v e  t o  ope ra t ing  energy'  requirements.  Therefore,  l i q u i d - f  l u i d i z e d  beds 
were e l imina ted  from f u r t h e r  cons ide ra t ion  f o r  s to rage  a p p l i c a t i o n s .  
When des igning  mul t i s t age  beds, t h e  bed s t a g e s  should be k e p t  a s  
shal low a s  p o s s i b l e  t o  minimize the  p re s su re  drop. 
Multis tage f lu id ized  beds, which have a l a r g e r  temperature re-  
covery e f fec t iveness ,  a r e  p re fe rab le  t o  s i n g l e  s t age  beds; however, increasing 
the number of s tages  may a l s o  increase  the  t o t a l  system pressure  drop. 
Mul t i s tage  counter flow systems have higherthermalefficiencythan 
mult is tage  cross  flow systems wi th  an equal number of s tages .  A s t a b l e  flow 
of s o l i d s  aga ins t  gases can be obtained by down flow pipes o r  overflow weirs 
i n s t a l l e d  between s tages .  Such mul t i s tage  shallow beds have successful ly  
operated i n  such u n i t  opera t ions  a s  continuous adsorption.  
TES Applicat ion I d e n t i f i c a t i o n  
A l a rge  number of i n d u s t r i a l  processes,  s o l a r  power generat ion,  and 
HVAC systems were considered f o r  p o t e n t i a l  app l i ca t ion  of FBHX f o r  TES. Due 
t o  the la rge  number of p o t e n t i a l  app l i ca t ions ,  they were grouped by u n i t  pro- 
cess  with s imi la r  waste c h a r a c t e r i s t i c s  (Table I).  Thus, a  se lec ted  FBHX/TES 
system f o r  a  u n i t  process i n  one indust ry  may a l s o  be adaptable t o  o the r  in-  
d u s t r i e s  with s i m i l a r  u n i t  processes. Flow char t s  were obeained f o r  the u n i t  
processes and energy balances performed i n  order  t o  evaluate  the  p o t e n t i a l  fo r  
energy recovery. 
In teg ra t ion  and Se lec t ion  
I n  order  t o  reduce the p o t e n t i a l  app l i ca t ions  t o  the  s i x  most pro- 
mising systems f o r  a  more d e t a i l e d  review, a  number. of c r i t e r i a  were se lec ted  
f o r  the processes. The c r i t e r i a  fo r  t h i s  ana lys i s  were: 
Waste stream temperature 2 260°C (500°F) 
Flow r a t e  2 283 m3/min (10,000 cfm) 
Annual ener recoverable from t o t a l  indus t ry  2 1.05 x 10 10 f3 W / y r  (10 BTU/yr) 
Need f o r  TES 
Proximity of energy source t o  use 
Unique benef i t s  such a s  po l lu tan t  removal o r  reduced plugging 
The s i x  app l i ca t ions  designated with an a s t e r i s k  (*) i n  Table I were 
chosen for  a  more d e t a i l e d  review. Five ' addi t ional  s e l e c t i o n  c r i t e r i a  were 
then es tabl i shed f o r  f i n a l  screening of  the  s i x  candidates.  The add i t iona l  
c r i t e r i a  were: ' 
r Adaptabi l i ty  t o  candidate process 
r Growth p o t e n t i a l  of candidate process 
Rela t ive  s impl ic i ty  of system when i n t e ~ r a t e d  with FBHX/TES 
Timeliness 
Acceptabi l i ty  t o  indus t ry .  
As a r e s u l t  of the  f i n a l  screening process the cement p l a n t  r o t a r y  
k i l n  and the  s t e e l  p l a n t  e l e c t r i c  a r c  furnace were chosen f o r  d e t a i l e d  techno- 
economic evaluat ion.  
TASK I1 - TECHNOECONOMIC EVALUATION 
The technica l  aspects  of the  evaluat ion f o r  the  ro ta ry  k i l n  'and 
e l e c t r i c  a r c  furnace appl ica t ions  of FBHX/TES systems a r e  near ly  complete. 
Each technica l  evaluat ion  included es tab l i sh fng  a p lan t  process flow config- 
u ra t ion ,  an opera t ional  scenario,  a  preliminary FBHX/TES design,  and para- 
metr ic  analys is .  
The process flow configurat ions f o r  each app l i ca t ion  (Figures 2 and 
3) a r e  s imi lar  i n  t h a t  the  TES charge cycle f o r  both designs uses ho t  exhaust 
gases t o  heat  the bed mate r i a l  (sand) i n  a  counter flow, mul t i s tage ,  shallow 
FBHX. The hot  s o l i d s  a r e  then s tored  i n  an insu la ted  s t r u c t u r e  u n t i l  the  
energy i s  needed. During the  TES discharge cycle the  sime counter flow, 
mul t i s tage  shallow FBHX is  used t o  heat  low temperature gases f o r  a  waste hea t  
bo i l e r .  The cooled s o l i d s  a r e  s tored  i n  another insu la ted  s t r u c t u r e  t o  await 
the  next charge cycle.  The e l e c t r i c  a r c  furnace app l i ca t ion  a l s o  includes a 
buf fe r  FBHX/TES t o  smooth the shor t  durat ion (2-3  h r )  pe r iod ic  v a r i a t i o n s  i n  
gas temperature before proceeding t o  the  long-term FBHX/TES described above. 
Options t o  e l iminate  the  separa te  buffer  a r e  present ly  being considered. 
The i n i t i a l  opera t ing  scenerio for  the  c e w n t  p lan t  requi res  approxi- 
mately 80% of the  r o t a r y  k i l n  exhaust gas t o  be s e n t  d i r e c t l y  t o  a  waste hea t  
b o i l e r  f o r  power generat ion while the remaining 20% is  used t o  charge the TES 
system. During discharge,  100% of the ro ta ry  k i l n  gases a r e  s e n t  d i r e c t l y  t o  
the  waste b o i l e r  while approximately 20% of the b o i l e r  exhaust i s  .recycled 
through the FBHX/TES t o  recover energy and added t o  the k i l n  gases a t  the  
waste h e a t  b o i l e r  i n l e t .  This r e s u l t s  i n  a  t h e o r e t i c a l  power production swing 
from 80 t o  120% of the  nominal generat ing capaci ty  without TES and allows 
s i g n i f i c a n t  i f  not t o t a l  reduction i n  peak power demand. 
The i n i t i a l  opera t ing  scenerio f o r  the  s t e e l  p l a n t  r equ i res  100% of 
the  e l e c t r i c  a r c  furnace exhaust gases t o  be s e n t  t o  the  FBHX/TES system during 
a charge cycle when a l , l  power i s  purchased a t  off-peak r a t e s .  When power i s  
purchased a t  on-peak r a t e s ,  both the  TES system and the  e l e c t r i c  a r c  furnace 
gases would be ava i l ab le  f o r  power production and reducing peak demand. 
A parametric ana lys i s  i s  being performed t o  determine the optimum 
FBHXITES design. A computer model was developed t o  determine the  e f f e c t s  of 
the  number of s tages ,  gas temperatures, gas flows, bed mate r i a l s ,  charge d i s -  
charge times, and p a r a s i t i c  power required f o r  operat ion.  
Work on the  economic-analysis has been i n i t i a t e d .  The est imated 
c a p i t a l  investment cos t s ,  annual opera t ing  c o s t s ,  and u n i t  energy cos t s  t o  
cons t ruct  and opera te  each model system w i l l  be determined. Cap i t a l  inves t -  
ment cos t s  w i l l  represent  the  t o t a l  investment required t o  cons t ruct  a  new 
system and w i l l  include d i r e c t  cos t s ,  i n d i r e c t  cos t s ,  c o n t r a c t o r ' s  f ees ,  and 
contingency. Annual opera t ing  cos t s  w i l l  represent  the  va r i ab le ,  f ixed,  and 
overhead cos t s  required t o  operate the systems. Unit energy c o s t s  f o r  each 
model system a r e  the  annual operat ing cos t  of  the system divided by the annual 
energy savings. A l l  c o s t s  associa ted  with the  waste hea t  b o i l e r  system and 
the f lu id ized  bed heat  exchanger TES system w i l l  be determined separa te ly  . 
The t o t a l  c o s t  of the  model system w i l l  equal the  sum of the individual  cos ts .  
CONCLUD LNG REMARKS 
The t echn ica l  f e a s i b i l i t y  of FBHX f o r  TES systems has been v e r i f i e d  
by ana lys i s  of two se lec ted  conceptual systems. I n i t i a l  r e s u l t s  f o r  the  
cement p lan t  ro ta ry  k i l n  i n d i c a t e  t h a t  the  d ive r s ion  of 20% of the  k i l n  
exhaust gases t o  a  5-stage FBHX~TES system during a 12-hr charge period allows 
power production t o  be increased 11% during a 12-hr discharge period.  Simi- 
l a r l y  the d ivers ion  of 100% of the  e l e c t r i c  a r c  furnace gases during an 8-hr 
charge cycle of an 8-stage FBHXITES system allows power production t o  be i n -  
creased 34% during a 16-hr 'discharge period. 
When the economic and trade-off  ana lys i s  a r e  concluded, we w i l l  be 
able t o  e s t a b l i s h  whether TES systems using FBHX a r e  economically v iab le  and 
i f  so, i d e n t i f y  one of the systems fo r  f u r t h e r  study o r  demonstration. 
TABLE 1 
POTELTLG &F'PLICATIONE OF FLUIDIZED BED HEAT WCEWGERS AS A FUNCTIOlr' OF 
LYIT PROCESSES OR CASTE NERGI' S T E L ' I  
Unit Process /Kaste  Energy S t r u m  Industrn* 
1. Xiln Exhaust Cases. Cl inker  Cooler W a u s t  Gases *camant ** 
Lime 
Sodium Carbonate 
Pulp N i l 1  
Zinc Oxid* 
Prlmary Alumin= . 
Clay and Ceramic Product8 
Phosphate F e r t i l i z e r  
2. Pe r iod ic  Ki ln  
3. S i n t e r  and P e l l e t  Machine/Cooler Exhausc 
Gases 
6. E l e c t r i c  Arc Furnucc Exhaust Gases 
5 .  Sola r  Brayton 
6 .  Reverberatory Furnace Exhaust Cases 
i. S o i l e r s  (HVAC) 
8. B la s t  fu rnace  Exhaust Gases 
9 .  Dryer Lxhausc Cases 
10a. Compressor Exhaust Air 
Clay 
Carmoics 
"Iron and S t e e l  
P r i m a q  Zinc 
Primary Lead 
*iron m d  S t e e l  ** 
I ron  Foundry 
S t e d  Foundry 
Fa r roa l loy  
Nonfarrous Foundry 
Secondary Xonfarrous Smolting and 
Refining 
Ref rac to r i e s  
*Primary Copper 
Primary Lead 
Nonferroue Foundry 
Secondary Sonferrous  Smelting and 
Ref ining 
I n d u s t r i a l ,  C o m e r c l a l ,  Res iden t i a l  
I r o n  
Primary Lead 
Secondary Nonferrous S rne l thg  and 
Ref ining 
Phosphate F e r t i l i z e r  
Clay and Ceramics Products  
Asphalt Paving 
T e x t i l e  Indust ry  
Pulp and Paper Indus t ry  
Food Induscr? (g ra in  drying)  
Chemical and Al l i ed  Produces 
Pneumatic *chinery 
Compressed Gas C h i l l e r s  (food indus t ry )  
lob. I C  Sngine Exhaust Gases Various I n d u s t r i e s  
11. D i s c i l l a t i o n  Colrmm Exhaust Screams 
1:. Wash-down Water 
Chemical and Al l fed Produccs 
Petroleum Refining 
Food I n d u s t v  
Textile Indus t ry  
13. Cupoia Exhaust I ron Foundry 
14. ZokeOven *Iron and S c l e l  
* Six applications selected for additional study 
** Two applications selected for detailed Technoeconomic Evaluation 
Cool 
E- Out 
Cool 
Solids in 
Hot 
Cool 
Solids Out 
Cyclone 
Separator 
Cool 
cool Gas Out 
Solidsin 
Hot J> Distributor 
Gas in + Plate 
Hot Gas in 
Cool 
Hot Secondary 
Fluid Out 
Brine 
Cool Secondary 
Fluid in I 1 Hot Secondary Fluid Out --, 
in Distributor Plates 1 1  
Hot I-J 
( F )  Brine in 1 
n g u r e  1 - Representative Configurations of Fluidized Bed Heat Exchangers 
Steom for Flectrlc Power b 
Dust Removol 
, Mde , 
303-F , a
Boiler (WHB) ~ ~ h . , ~ ~ t  
Dischorge 
Slock 
Wosle Heot 
il r ( ) . , t  0 
Figure  2 - Conceptual  FBHX/TES System i n  Cement P l a n t  Rotary  K i l n  
Electric /yC Power 
Row Motmriols 
Preporotlon 
I 
Row 
F i g u r e  3 - Conceptual  FBHX/TES Spstem i n  S t e e l  P l a n t  E l e c t r i c  Arc Furnace 
------ 
------ 
Moterials 
r 
I 
l u t b i m  - Genemtor 
I 1 
He01 
Erchonger 4 Mlxer -
t Solids In  
Multi-Stage 
FBHX 
Cnnhing 
I lWJDF  ode* Solids Out 
Blend f Discharge Mode 
Pm - I ~or t ton  of 
Healer WHE Exhnusl 
-5lnglm K i ln  Exhousl Gas 1 Clinker Cooler Eahoust 
Sloge Cii 400°F to W M  
Cooling Air 
- h b i e n t  
'Ow 
~ n d l n g  
Blending 
( h l l e r )  Dul l  
Removol 
Steel Arc 
Furmce 
BL'int ------ 
Charge 
@80 - 30M)'F 
- 
Mixer 
Thermol 
Energy 
Sloroge 
( Duller*) 
- 
1300'F 
Steel Arc Avcrop  
Furnace 
Discharge 
------ 
Mcde 1 I Mode [4 
-------       .c Multi-Slog* So ids I n  
*Buffer: Smooth out fluctuolions 
I n  tsmpemture from 
cyclic opcrotlon of steel 
arc furmces. 
**Peoklng: Srrppllcs oddi t Ian1 thcnnol 
mnergy w k n  MI ermgy from Mode Mode 
furnaces is not wfflclmnt Portlon of Boiler Erhoust 
10 rmmt &mod.  
1300.F 
C h a w  ) 4 ~ischorge 
----- - 
- - - - - - - 
------. 
FBHX 
Sollds O u l  


Thermal energy storage systems using fluidized bed heat exchangers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server