sulfuric acid double contact
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M O L T O X ~ CHEMICAL AIR
SEPARATION
SYSTEM
- A PROGRESS
REPORT
Donald C.
Er1ckson
Energy
Concepts
Co.
Annapo11s, Maryland
W111iam
R.
Brown
and
Br1an
R.
Dunbobb1n
A1r
Products
and
Chem1ca1s,
Inc.
Allentown, Pennsy1van1a
Robert G.
Massey
U.S. Department of
Energy
Wash1ngton,
D.C.
ABSTRACT
A
new
low energy route to tonnage
oxygen
product1on, the O L T O X ~ system, 1s now
commenc1ng
p110t plant test1ng. The process,
1ts h1story, and potent1a1 app11cat10ns will
be
descr1bed, 1n add1t1on to recent results of the
p110t
plant
test
program. Future development
needs and plans for commerc1a11zat10n w111 be
outlined.
INTRODUCTION
More than 300,000 TI of large tonnage
cryogen1c
oxygen
plant capac1ty was bu11t 1n the
1960's
and
1970's. The two-th1rds st111
operating w111 consume about $20 b11110n (1985
) of electr1cal energy 1n the next decade. The
HOLTOX
m
chem1ca1
a1r separat10n system
1s
being developed as a cryogen1c oxygen plant
replacement wh1ch w111 use energy
at
less than
one-half of th1s
rate.
A1r separation by cryogen1c d1st111at10n was
1ntroduced
90
years
ago
by
Carl
von
L1nde
of
Germany
and cont1nues to be the choice for
tonnage
oxygen
production. Current des1gns
requ1re 25
less
energy than plants
built
in the
1960's
and
1970's. The HOLTOX chemical air
separat10n system is being developed to offer a
lower
cost
oxygen
a1ternat1ve for
new oxygen
requ1rements by revolutionary rather than
evo1ut1onary development. The process requires
up to
40
less energy use than today's
commerc1al oxygen technology. This translates
into a five to th1rty percent reduct10n in
oxygen cost. This 1ncludes both cap1tal and
energy
costs.
In
1979,
Donald C.
Er1ckson of
Energy
Concepts
Company
received the first
of
several U.s.
patents for a chemical a1r separation process
for tonnage
oxygen
product10n.(1) Th1s new
method of
produc1ng
oxygen
uses a molten m1xture
* HOlTOX
1s
a trademark of
A1r
Products
and
Chemicals Inc.
of
a1ka11
n1trates
and nitr1tes to
chem1ca11y
react w1th oxygen 1n
compressed
a1r.
Heat1ng or
depressur1zation then
releases oxygen of greater
than
99.8%
pur1ty
1n
a revers1ble react10n. The
major port10n of the energy
used
to compress or
heat the a1r 1s recovered
from
the waste
nitrogen exhaust.
With support
from
the U.S. Department
of
Energy, Mr. Er1ckson proved his concept 1n a
bench-scale unit that produced 6 liters per
m1nute
of oxygen.(2)
In
1982 Air Products
and
Chem1cals, Inc., in a cost-shar1ng,
cooperative agreement w1th the U.S. Department
of Energy, undertook the cont1nu1ng development
of the process,
now known
as the MOlTOX
oxygen
system.
Dur1ng Task
1, laboratory support
stud1es provided technical 1nformat10n on molten
nitrate/n1tr1te
chem1stry
and
on the corros10n
res1stance of mater1a1s of construct10n.(3)
In January 1985, the dec1s10n was made to
proceed
w1th
Task
2, the construct10n
and
operat10n of a 0.25 ton per
day oxygen
p110t
plant. This
$6 m11110n,
four-year project
1s
enter1ng 1ts
f1na1
year w1th commencement of
p110t plant
test1ng. The
twelve
month
p110t
plant exper1menta1 plan
first calls
for 'Proof
of
Concept' operat1onal confirmation
and
then
for acquisition of engineer1ng design data for
scale-up
and
optimization for the next
development phase.
PROCESS
DESCRIPTION
The MOLTOX system is based on the reversible
react10n of
oxygen
with
sod1um
and
potassium
nitrite
to
form nitrate.
This reaction
can
be
used
in
one
or both of
two HOLTOX
system
salt
loop types, Pressure Swing Absorption (PSA)
and
Thermal Swing
Absorpt1on (TSA). The basic
operating modes
are:
ESL-IE-86-06-78
Proceedings from the Eighth Annual Industrial Energy Technology Conference, Houston, TX, June 17-19, 1986
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1. PSA - (PRESSURE SWING ABSORPTION)
1.
Pure
Pressure
Swing
- For 1ntegrat10n w1th
the pressur1zed gases
of gas turb1ne power
plants.
2.
Pure Thermal Swing - For 1ntegrat10n with
the heat recovery and
steam generation
section of
industrial
and utility
steam
boilers.
2.
TSA -
(TEMPERATURE SWING
ABSORPTI0r-N,"-)--+-_"",
3. Combined Pressure
For any application
and Thermal Swing
in wh1ch heat
and
pressure energy are
avallable.
Simplified process diagrams of the two salt
loop types are shown 1n F1gure 1. These
d1agrams show the absorber and desorber salt
flows, the gaseous a1r
and
product flows,
and
the integrat10n of the salt loop w1th external
processes. For e1ther type of MOlTOX system
I
salt
loop, dry,
C02
free a1r enters the
I
absorber
at
a temperature of
783
to
922K
(950 to
I
(950F)
1200F)
and
a pressure of 0.41 to 1.2
MPa
(60 to
I
186
ps1a)
and 1s
contacted with the molten
=
INTEGRATION
I
O
MEANS WITH
-c;;z-joABSORBER
salt.
The oxygen
reacts chem1cally w1th the
EXTERNAL
salt (N02
+
1/202
N03)
and
1s removed w1th
PROCESS
the salt from the bottom of the absorber. The
Figure 1
n1trogen
and
1nert gases, along with some
Integrated
l T X ~ System
Salt
loop
un
reacted oxygen, are
removed
from the top of
the absorber
at
essentially the same pressure
EXISTING
and
temperature as they entered. The molten
500
CRYOGENIC
salt
from
the absorber flows to the desorber
0,
PLANT(S)
where the chem1cal reaction 1s reversed
(N03
N02
+ 1/202),
and
gaseous oxygen
is
released from the salt
and
removed
as
product.
400
The reversal of the chemical reaction in the
The
salt 1s
c1rculated around th1s
TSA
loop by a
Cl
100
a:
pump
operat1ng
at
the
783K
(950F) salt
LU
temperature.
z
LU
For
the PSA salt loop, the pressure of the
o
L ~ 2 4 L . . . . . L 6 . . . J 8 1
molten salt from the absorber is reduced across
the pressure letdown valve before the salt
HEAT EXPORT (MM BTU/TN 0,
enters the desorber.
The
pressure of the
desorber is controlled by the gaseous oxygen
' - - -MOLTOX
PROCESS TYPE--
pressure through a vacuum oxygen compressor.
PRESSURE
THERM L
The salt 1s removed from the desorber by a salt.
SWING
SWING
pump and
rec1rculated
back
to the absorber
at
F1gure 2 -
Energy
Advantage for Integ ated
the necessary pressure for recontact with M O L T O X ~ Cases vs.
Cryogen1c
Plants
compressed a1r.
497
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l1mlted heat aval1abl11ty for certaln TSA
HOlTOX process app11catlons led to the
deve10pmentof p ~ o s s des1gns for
ccimblned
PSA/TSA and. TSA/PSA HOlTOX
systems/:F1gure 2
graphIcally summar1
zes
the
des19n flex1bll l tyof
these
HOllOX
systems
by
show1ng
the
total
energy
requIred per ton.of
oxygen
versus the heat
1nput/output for the var10u( desIgns. The
thermal
slo/1ng
HOllOX system ut1l1zes the
least
net energy and cogenerates steam. Th1s f1gure
also
shows that
the net energy requ1red for
HOlTOX
system
oxygen
production
1s
substant1a11y
below that for the cryogen1c process. Exlst1ng
plants
were
largely bul1t 1n the
1960
to
1973
perlod
and
requlre ln excess of
450 KW
per ton
of oxygen,
whl1e new oxygen
cryogen1c plants
can
be
deslgned for about
350 KW
per ton of
oxygen.
POTENTIAL HARKETS
Electrlc
power
ls forecast to cost 7.5t/kwh
(1985 $)
ln the U.S. ln the mld-1990 s, when the
MOLT
OX system will
be
commercialized. The
MOlTOX oxygen system ls projected to
be most
competitive
wheresignlficant
process heat
lntegration
can be
achleved. for
most
app11cations, a 30 to
40%
reduction ln
total
energy 1s anticlpated,
compared
to new
e1ectrlc
drlve cryogenlc plants. Slnce
65%
of the cost
of oxygen from cryogenic plants 1s energy
related, use of the
HOlTOX
system results 1n a
projected
12
to 23% improvement over new
cryogenIc plants. This
HOlTOX
system
oxygen
cost improvement ls shown graphically in
Figure 3.
70
60
i=
SO
0
C l
U
Z
UJ
Cl
40
x
0
30
20
2
4 6 B 10 12
ELECTRIC ENERGY COST /kwh)
Flgure 3 -
Oxygen
Cost
Comparison
$600
psia,
9 9 5 ~
Purity
(l)New
1000
T/o Plant;
. .
15 Year,
100%
Capacity,
340 o/Yr
98
Figure 3 also
shows oxygen
~ o s t s from
ex1st1ng (circa 1960/73) fUlly depreclated
cryogenlc
oxygen
plants. Replacement of
exlsting cryogenlc o x ~ g e n p1antsservlng the
steel and
chem.iea
1 1ndustries represents
one
1mportant market opportunity
..
A
good example
ls
lntegrat10n with-blast furnace off-gas boilers
at
integrated steel mi11s.(4)
Twenty
percent
of the offgas to the existlng bol1ers ls
dlverted to a
new
steam/salt
heater bol1er
at
the
HOlTOX oxygen
plant.
The
remaining 80% is
burned in the existing bol1ers, whlch
results
ln
lower stack temperature and
more
steam
generation. Thls HOlTOX plant could supply
approximately half of
an
lntegrated steel ml11 s
oxygen
requirements, whl1e reduclng the ml11 s
electrical energy consumptlon.
Emerging
new
oxygen
markets also are
candidates for
MOLTOX
process
lntegratlon.
Several applications (oxygen enrichment of coal
for furnaces and bol1ers, refinery fluidized
cat-cracker
catalyst
regenerators, sulfur
recovery plants,
and oxygen
secondary reforming)
have
sufficient
heat available to provide the
entire
energy requirements for a
HOlTOX
TSA
plant.
New
applications with very large oxygen
requirements (coal gaslficatlon for synfuels
and/or combined cycle power generation; and
coal-based direct smelting of iron) have enough
available heat to provide for a combination
HOlTOX TSA/PSA plant.
PILOT PLANT
In
January
1985
the declsion was
made
to
proceed with
Task
2, for the construction
and
operation of the
pilot
plant. The areas of
technical uncertalnty to
be
addressed
by
pl10t
plant operation include:
TSA/PSA and TSA modes of operatlon
Salt
losses (vapor, corrosion,
salt
stabllay)
Absorption/desorption kinetics
Salt
loop equipment designs
Adequacy of materials of construction
Long-term operability,
and
Gas purity, impurities,
and
by-products.
Consideration of the above objectives led to
the p110t plant depleted in the slmp11fled
process flow diagram
shown
in Flgure 4. Thls
flowsheet includes a slngle absorber, a slng1e
desorber, a
salt pump,
a
salt
cooler,
and
a
salt/salt heat exchanger. Thls equtpment ls
sufflcient
to
test
all
key
parts of the thermal
swing
HOLTOX
process.
The materials of constructlon for the pilot
plant were selected based on corroslon test
results from Task 1.(3,5) Our
estlmate of the
maximum
use temperature for
common
engineering
alloys is given below.
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Alloy
Maximum Use
Temperature
Carbon
Steel
840F
316 SS
1150F
Incoloy 800
1250F
Inconel 600
1300F
The p110t plant s1mp11f1ed flow d1agram
shows
expected operat1ng temperatures along
w1th
the recommended mater1als.
The
p110t plant w111 allow further study of
the corros1veness of the
salt. The
corros10n
w111
be mon1tored
w1th
v1sual and ultrason1c
thickness measurements of vessels and p1p1ng;
1nstallat10n of corros10n
coupon
racks and
corros10n probes; and
1nstallat10n
of
p1pe
spools of test mater1als. The mater1als
be1ng
tested are those that can w1thstand hot,
oxid1zing cond1tions
and
1nclude sta1nless
steels
and h1gh nickel alloys wh1ch have shown
good performance in ear11er bench
scale
corros10n
tests. Bulk
n1ckel alum1n1de
alloy,
developed by Oak R1dge Nat10nal Laboratory,
and
FECRALLOY steels, developed by Harwell 1n the
U.K., are both cons1dered strong cand1dates for
serv1ce
1n
the h1gher corros10n areas of the
un1t. Ceramics, such
as h1gh
dens1ty fused
alum1na and z1rcon1a,
are also
under study, as
are var10us coat1ng techn1ques. Of part1cular
interest
are alum1niz1ng, MCrA Y and N1-Al
coatings.
The p110t
plant w11l
allow
tests
under salt flow cond1t10ns that resemble
commerc1al operations. Salt
samples w111 be
taken per10d1cally to mon1tor salt chem1stry and
corrosion product accumulat10n.
The
proposed t1metable for the f1rst twelve
months
of p110t plant operat10n 1s shown
on
the
Exper1mental Plan (F1gure 5 .
Th1s
t1metable 1s
broken into three phases. Phase
A,
Proof of
Concept,
w111
demonstrate steady-state operat10n
of the absorber/desorber comb1nat10n
at
a s1ngle
cond1tion for a long per10d of
t1me
(durab111ty
run). This w11l also ver1fy the des1gn 02
production rates, product pur1t1es,
and
energy
consumpt10n; and w111 determ1ne the
rate
of
corros10n
1n
various
parts
of the
absorber/desorber system. Phase
B,
Opt1m1zat10n, w111 probe the poss1b111ty of
1mproved process economlcs at more severe
operat1ng cond1t10ns. Phase
C,
Parametr1c
Stud1es, w111 def1ne the
effects
of the major
process var1ables, 1nclud1ng absorber pressure,
desorber pressure, absorber 1nlet temperature,
and
molten salt circulat10n rate/a1r feed
rate;
and prov1de the eng1neer1ng data needed for
scaleup and des1gn of the sem1works plant.
PILOT
PLANT
RESULTS
The p110t
plant started up 1n
March 1986.
The 1nstrumentat10n and mechanical operat10n
were
checked and the Run I absorber column
hydrau11c tests
showed
that the column could
operate
successfully
at des1gn cond1t10ns
w1thout flooding the column.
Sod1um perox1de catalyst was added to t e
salt
and
the low temperature oxygen generat on
tr1als
of Run II began.
The
plant ach1eved 0.12
T/D of oxygen product10n with 99.9 02
purity. Th1s
Is
92
of the theoret1cal
(equ111brum) 02 recovery for the 1130F
desorber and 930F absorber operat1ng
temperatures.
The un1t performed well for 4 days, at ~ h c h
t1me
the
316
sta1nless
steel
centr1fugal
fa11ed due to corrosion, cav1tation or a i
comb1nat10n of these processes . A redes1gned
pump
with a
low
cavitat10n potent1al impellrr
and Inconel 600 mater1als of construct10n
WpS
ordered, and
an
exper1mental program was
developed to separate the
effects
of c a v t a ~ n
and
corros10n 1n the
pump.
This program
was
undertaken and completed 1n May 1986.
As of May 28 1986, the p110t plant
1s
undergoing a planned two week turnaround.
old salt charge
1s
being replaced
and d d t ~ o n l
corros10n spool p1eces are be1ng
1nstalled Wor
test1ng
at
actual salt flow cond1t10ns.
base case des1gn and durab11ity run will i
commence
1n
early
June.
i
DEVELOPMENT PLAN I
In
parallel
with pilot plant operation,
separate laboratory and bench-scale f
exper1mentation
will
address salt losses,
k1net1cs, a1r pur1f1cat10n, alternative salts,
and better mater1als of construction.
Pro
ess
heat
1ntegration
and optimization
will
be
addressed by further engineer1ng stud1es a ter
the Proof of Concept p110t plant operat1jn.
Results from these laboratory and eng1neer ng
studies
will
be
1ncorporated into future p ot
plant
operation plans.
The
p110t plant ha been
designed for easy modif1cat10n, so that th se
future process improvements can
be
tested
nd
confirmed.
Support
by
the
DOE
for the MOLTOX proc ss
development w111 end
after
complet10n
of the
1n1tial
twelve month p110t
plant
operation.
The next phase of development
111
requ1re construct10n
and
operat10n of a no 1nal
50 ton per
day
semi-works plant, as well a
continued p110t plant and laboratory work. Air
Products
will
seek development support fro
partners who are e1ther oxygen users or
suppliers
of oxygen us1ng technology and w 0
can
also prov1de high temperature metallurg1ca
expert1se. The areas of technical uncerta nty
to be addressed by the semi-works plant ar
plant scaleup and process heat 1ntegrat10n at
an
oxygen
us1ng host
site.
ACKNOWLEDGMENTS
The authors
would 11ke
to thank Air Pr ducts
and Chem1cals, Inc. and the U.S. Departmen of
Energy for perm1ss10n to pub11sh th1s pape
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0783
SALT
__ SEPARATOR
('200'
20
PSIAI
I I I
07 02 I
DESQRBER
T
07 80 I
r - ...L -
FLUIDIZED
SALT
1215F
SAND
HEATER
I
EPARATOR
i
I
11111111
I
11111111
11111111
I
I
I
I
t
I
tTl
i
0540
SALT SALT
EXCHANGER
10.30
05 41
SALT PUMP
SALT
COOLER
05.09
AlA 0
1
EXCHANGER
AlA
05 10
AIRIN
EXCHANGER
FIGURE 4
MOL TOX M PILOT PLANT FLOW DIAGRAM
c.w
LEGEND
CARBON STEEL
316SS
OR
304SS
INCOLOY 800H
INCONEL 600
to O
~ ~
?
....
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EXPERIMENTAL
PLAN
REFERENCES
M O L T O X ~ PILOT PLANT
1. Er1ckson. D. C.
S e p a r a ~ l g Q
of
Oxygen
rom
OVERALL
Gaseous H1xtures W1th
Mo,t@n Alka11
Met
1
SCHEDULE
OBJECTIVES
S,alj:,s" U.S. Patent 4.132.766; 2 Janu
ry
12 STEPS TO SUCCESSFUL ENERGY PROJECT K A N A G E H E N t 9 7 , ~ l t f ~ l f 6
4.2B7.170;
~ g 6 0 . 5 7 8 )
A.
~ ~ ~ r a t i o n
Anderlon. SC
.. ..
2 h . ~ r t ~ ~ n . , D . . .
'Oxygen Product1on by
he
A C O U R A 1 J h ~ r f . ~ ~ ~ A R
RESPONSE R ~ f ' t l t t - ' p r 8 e J ~ ~ . F1nal 6 ~ l t o r t
H.
~ d ~ g e
Grant
Company,
Bixlon,
T N ' O O ~ / C S / 4 0 2 8 7 ~ T 2 ' ( O t 8 j 0 1 2 8 4 7 ) ;
February
1983.
Steady state of operat1on
FUEL C L L ~ 1 t h
1100F
desorber.
Close
3. Archer.
R.
A.
and Dunbobb1n. B. R "Pllot
--mater1aland
energy balance
Plant Development of A
Chem1cal
A1r
Seuion
cwtftaat'gefl.
I i t ~ ..
Konlanto
C O l I p a n Y 6 ~ c Y
Process." F1nal Task I DOE
Report
DE-AC07-82CE40544; May
1985.
4
Months
FUEl. c ~ b S e N 8
A t S l _ ~ m C H N O L O G Y , Douglas M. Jewel,
M o r g H w k l i i t l l l M l r o ~ c J R c 1 ;
Center,
M o r g ~ t e r J t R J t l < J 6 f ) h l ,
'8'.' 'R' 'B"r"o\on, ~ ? 7 R .
pur1tles.
and
energy Cassano.
A.
A
.
and
Massey.
R.
G
.
THE O N g ~ ' I U ' t I l . o o E f D r c e u R l a n O SYSTEM, Root
_ _
< t m n J J S ~ t e m Integrat10n for The i
John(,nOeMtlluo.iI.rtaren A.
Trimble,
Gas R e ~ r f l l t 8 l ~ t ' f l ' f e O x y g e n aniHeam." AICh
Chicago,
IL
. . . . . . . . . . o y I l 1 P 0 5 . , u 5 e f . , ~ lIugust 1985.
5 ~ 8 t t l e ,
Durab1l1ty run. Long term
P O T E N ~ A t s r t o i
,oiLeOltU. IN. REFINERIES A N D 5 C H 5 Q i ~ ~ L ~ . W
T1tcomb. J. B
.
PLANt8}acrili;Allllt".naddtlred
Roach,
Los A ~ ' f l f 1 n g e r .
H.
T
. and D ~ n P o b b 1 n .
B
,
National Laboratory, LOl Alamos,
NK
~ r r e s 4 e f t 4 f t H o ~ t e n N 1 t r a 1 ~ ~ N 1 t r 1 t eSalts"
B
Opt1m1zat1on _ Journal of Metals - July 1985.
r
PLANNING ACOMMERCIAL FUEL CELL
INSTALLATION, Ji
ie R.
J l o w ~ M . ~ c Q e f l 1 g ' 9 4 Y I i 8 h t e l N a t 1 o n ~ 1 Inc.,
San
F r a ~ ' l w ~ t t : w l . r . i 1 t ~ .
glJt1
ty
.aod..
633
energy use for
Base Case B
E N C O U w . b i R ; I i ~ t . L ) DEMONSTRATIONS
OF
FUEL CELL
APPLICATIONS,
JOleph
M.
Anderlon,
I n d u ~ t r i a l
Fuel Cell Association,
Lake
2
Months
643
1
t h a i l ~ 1 , e ' t f A , 1 . R J R r , q V . ~ < t . Q R ~ r . < i t t n
at more severe operat1ng
cond1t1ons (1250F
C O M B U S T l o W ~ C Y HEAT
RECOVERY
ho. .
&.raRleJ:f,w.l
Sess\on
~ l ~ r ~ ~ o s l ~ ~ n
A. Mozzo, Jr . Aaerican ~ t a n d a r d ,
Inc.,
pallcU'Tar * e ~ \ i h
NY
concentrat1on '
COGENERATION
AT IOWA METHODIST MEDICAL
CENTER.
Cabot
Thunem,
and Steve
Schebler,
Stanley ConsultanU, Inc., Muscatine,
IA
and Glenn Love,
Iowa
Methodist Medical Center,
Des
Moinel, IA
677
I N D U s t i p ~ e c O b E N E R A T I O N
APPLICATION, Martin
A. Mozzo, Jr .
American Standard.
Inc.,
New York.
NY .. . . . . . . . . . . . . . . . . . . . .. . . . . . . 684
x v ~ P l
ESL-IE-86-06-78
Proceedings from the Eighth Annual Industrial Energy Technology Conference, Houston, TX, June 17-19, 1986