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HCOS
The
25th
International
Conference
on
Efficiency,
Cost,
Cptimization
and
$imulation
of
Energy
conversion
systems
and
processes
Perugia,
June
2Oth-June
29th,2012
Book
of Proceedings
-
Volume
ll
Edited
by:
Umberto
Desideri,
Universita
degli
studi
di
perugia
Giampaolo
Manfrida,
Universita
degli
studi di
Firenze
Enrico
sciubba,
universita
degli
studi
di
Roma
"sapienza"
2012
SnprEr{H
uNrvlRSt't'A
ur l{O,un
ECOS 2012 - TFtr 25rH INTERNA'IIO}'IAL CONFERtr}{CE O},7
EFFICMNCY' COST, OPTIv*ItrZATION, SIh,{IIII-ATION Ah]I] EN1/IRONh,iENI.AL Ih,fFACT OF. ENERGY S}-STE]V{S
JI-INE 26-'29,
2012,
PERUGLA,
ITAI-Y
EDITED BY LIh,ItsERTO
DESIDERI,
C]LAfu{I'AOI-O
h,LANFRIDA, ENRICO SCIITBBA
FIRTNZE
LrNr\aERSITY
PRESS,
2012,
ISBN ot'.tLxNE
: e78-88-66
55-322-s
PF.CTCTEDINGS OF ECOS
zOIt -'trftrX
25ttr [NifnRN.Vl'nOt'r-AI-
CON};IRENCE
ON
EFFICMNCY. COST., OF'IITfl7ATION, Str},fi-TLAT.ION
AND 8N1'N.POI\hffi\-{..\N-
I}flPACT OF ENERGY SI'STEh,{5
-f-[,xNF
?.{--r- 2f)
. 20 12, F'ERLICLA, ITALY
Energy
Integration
and
Cogeneration
in Nitrogen
Fertilizers Industry: Thermody
nam
ic Estimation
of the
Efficiency, Potentials,
Limitations and
Environmental
lmpact.
Part
1:
Energy Integration
in
Ammonia
Production
Plants
Zornitza Kirova - Yonlunova
Deparfinenl of'lnot'gutic T'echnolog7,,
('niversilt, " P,'q/.' .l.s.sen
Zlcttu'ot"', ,90I0 Botn'gct.s,
Bulgatia
a i l ; z/;
i rr.n,o
;
t! h
l t r .
lt
q, zo
rni txt l;
i rowtt ti vt lt ts rt. t:o. t r lt
Abstract:
The nitrogen fertilizers
production
is
an energy
intensive industry
branch. However,
from
a thermodynamic
point
of view, tre basic reactons of the nitrogen fertilizers
produclion
processes
are exothermic
and he
overall reactions of both
process
routes
(ammonium
nitrate
and urea
production
routes)
are also exothermic.
This means
hat, if all these reactions could
be performed
in a thermodynamically
ideal way and at he
reference condilions, some heat and/or power could be obtained from trese reactions,
rather than
consumed. However, mosl of the reaction
$ages are limited
by the chemical
equilibrium
and readion's
kinetics, which require high pressures
and temperatures,
hence, big quantities
of shaft power and heat
(steam)
have to be consumed. In modern
energy-integrated
ammonia
and nitric
acid
plantsthe
heat of he
exotrermic dremical reaclions is used to generate
mechanical
work (by a steam cyde or/and by a gas
turbine cyde)
to ddve compressors and ofrer machinery.
lf needed,
an extra amount
of fuel is burned to
satisfy all tre requirements of energy
in the plant
itself
and/or
in the overall
fertilizers
produclion
complex.
The
problem
iswhetheritwould be moreeffedive to burn
some
quantity
of fuel
to provrde
a chemical
plant
with
powerand/orsteam
in the
energyintegrated
dremical
plantitself;
in an utility
boilerorin
a CHPplantat
the same industrial site.
The
goal
of thiswork isto analyse the
efficiency
of the energy
integration
in a nitrogen
fertilizersproduction
site, induding ammonia and nitric acid
plants.
The main
issue
is how to distinguisl'r
the technological
and
energy
conversion
processes
in order to estimate
their
efficiencies
separately
despite
the strong integration
of trese processes
and the complexity of modern energy-integrated
dtemical
plants.
The approach
presented
in this work is to define
a model
of the
ammonia
production
process
that
enables
specifying separatelythe
theoretical minimum
of energy and
feedstock
consumplion
in the chemical
process
and in the energy conversion
processes
(especially
sfraft
vr,ork
genemtion).
Then, using real data for
efficiency
indices of both
groups
of processes,
the next $ep is
to examine
the influence
of
these indices on
the energy (and exergy)
consumption
and to specify
tre sets
of parameters
corresponding
to the more
efficient
kind of plant,
eneqy integrated
or non-integrated,
respeclively.
In Pad 1 of this wor( ammonia
produdion
plants
are seleded as a subject
of analysis.
Ke
ywords
:
En ergy integ rati on, Cog en eration,
Am moni a, Effi
cien
cy,
EnM
ron menhl i mp a ct
1. Introduction
In power
industry the Combined
Heat
and
Power
(CHP)
is defined as
a simultaneous
generation
of
usable
heat
and
power
(electricity
or
mechanical
enerry)
in
a single
process.
CHP
is
also
referred to
as cogeneration
[1].
For many
years
the CHP generation
has been applied
predominantly
in the chemical
industry,
petroleum refineries
and other
large
industrial
sites.
ln 2005
about
50%
of thesteam
and
hot water
demand
inEIJZT
industry
was satisfied
by CHP
[1]
138
In chemical
industry an enerS/-inteEated chemical
plant is a well-fitted combination of a chemical
and a power plant. The waste heat of the exothermic chemrcal reactions is used to generate
mechanical
enerry (bV a steam
cycle or/and by a gas
turbine cycle) to drtve
compressors,
punps,
fans, etc. In some cases the term "cogeneration"
is also used [2], but only if electricity is
produced
[3] The ener$/-integration concept enables the chemical
plants to be energetically self-sufficient
and to consume only feedstock
and
fuel
and
rather
less
electricity
A vigorous
gowth of cogeneration
in the chemical
industry began since
the first large
single-train
eners/-integrated
ammonia
plant was put into operation
in 1965
[a] For the last five decades
the
energ/-integrated chemical
plants
have
been
coffrmonly
used
in the bulk chemicals
industry. Nearly
all modern
ammonia, methanol and ethylene
plants over
the world are enerS/-integated
[4,5]. The
developing of high-pressure
(up to 30 MPa) multi-stage
centrifugl compressors
enabled the use
of
steam- and gas-turbines
to drive all machinery, which in turn enabled designing large capacity
plants
as single-train units.
However, in some
integrated
plants the available
heat of reactions cannot
satisfy all deman'ds
and its
temperature
is relatively low. To solve this problem, in earlier
designs
an extra amount of fuel was
burned in an auxiliary boiler (or in the process furnace itselfl to satisSr
all the requirements for
power and steam
in the plant.
The main question tht should be answered
is whdher it would be more effective to burn some
quantity of fuel to provide a chemical plant with power andlor steam in the eners/-integated
chemical
plant itself, in a utility boiler or in a CHP plant at the same
industrial site.
In many cases
the answer depends mainly on the demand of steam and power in the overall
production
site, on the export
/ impoft opportunrties
of electric
power, etc.
The relative
efficiencies of energ,-integated
and
non-integated
plants
depend
strongly
on the sign
of the reaction heat of the main chemical
processes. According
to this, three kinds of chemical
plants
could
be distinguished.
o main
reactions
are exothermic,
i.e.,
the plant is an energy
source;
e)€mples are
nitric acid and
sulphuric acid
plants;
. main reactions
are endothermic,
i.
e.,
the plant is an
energy sink,
examples
are
ethylene
plants;
. some of the main reactions
are exothermic and some
are endothermic;
the overall effect is near
neutral, e)omples are arrunonia and methanol
plants.
The nitrogen fertilizers production is selected
as an appropriate subject of analysis, as it includes
two different kinds of plants: ammonia and nitric acid production processes,
both existing in
ener
g/ -
int
egrat
ed and non- int e
grat
ed vers
ions.
The goal of the present work is to analyse
the efficiency of the eners/ integration in a nitrogen
fertilizers
production site, including
production of intermediates:
(ammonia and nitric acid) and
final product (ammonium nrtrate).
The subject of the frst part of the analysis is the energr
integration rn ammonia
production
plants.
The exerg, method [8] is used in both parts of this work in order to compare
the efficiency of
eners/-integrated
and non-integrated
ammonia
and nitric acid plants, as well as to estimate
the
overall efficiency of a whole nitrogen fertiltzers production slte.
In some
previous
works [9-11] *e have compared
the efficiencies
of enerry integrated
and non-
integrated
ammonia
plants [9] and
nitric acid
plants
[10] usingsome
Second
Law-based
(exergy
and
cumulative
exergy) ndices and operational data from real plants. The results showed
that non-
integated ammonia plants are
definitely more efficient than energy integrated;
the results for nitric
acid plants are qposite. A generalized
conclusion was made that the eners/ integration
is more
advantageous
in the case when the efficiency of the ener5/ conversion process (shaft work
generation)
is higfrer
than the efficiency of the chemical
process and vice versa. However, these
results could be questionable
to some extent because
they were ohained by processing
data for
similar, but yet different plants, and the difference of some of the process parameters in the
compared
plants miglrt have an effect on these results.
The considerable
recent achievements both
in chemical technologr and in enerry conversion processes and machinery, which undoubtedly
influence
the efficiency of the energ/ inteEation, also
motivated
the present study
139
The main
problem
is
how to distinguish
the
technologrcal
and
enerS/
conversion
processes in order
to estimate
their efficiencies
sepaiately
desprte
the strong
integation of these
processes
and the
complexity
of modern eners/-integated
chemical
plants.
Hence,
we need
to define
a model
of the
ammonia
production
process
that enables
specifying
separately
the theoretical
minimum
of enerS'
and feedstock
consumption
in the chemical
process and in the energy conversion
processes
(especially
shaft
work generation). Then, using
real data
about
heat and
exer$/ losses and
efficiency
indices of both goupr of proresses,
the
next step
is to examine
the influence
of these
indices
on the
enerS/
and exerg, consumption
and
to specify
the sets
of parameters corresponding
to the more
efficient
kind
of plant,
eners/
integated or non-integrated,
respectively.
2. Ammonia
production
background:
basic
reactions
and
heat
effects
The commercial
manufacture
of ammonia
since
its beginning
in 1913
is based
on the catalytic
synthesis
of ammonia
from a highly purified mixture
of hydrogen
and nitrogen.
Although the
synthesis
of ammonia
is an exothermic
reastion, to obtain
this mixure,
especially
hydrogen,
a lot of
energ/
is necessary
to sp
lit a
molecu
le of water,
which
is the main
hy drogen-contain
ing source.
If a
part of the lrydrogen
ii sryplied by another
hydrogen-containing
feedstock,
like hydrocarbons,
in.rg, requirements
are
lower.
Thus
the most
favourable
feedstock
for ammonia
production
is the
natuial
gur
lCUo)
because
in this mse
only a
half of the
hydrogen
is obtained
from
water.
However,
the
hydrogen
production
from hydrocarbons
and
water
is
a strongly
endothermic
process,
hence a considerable
amount of higfr temperature
heat is necessary
to be introduced
into the
process,
usually
ohained
by burning
of some
quantity
of fuel
with air.
The combination
of both steam
reforming
and burning
processes
enables
to obtain
the hydrogen-
nitrogen
mixture
directly,
avoiding
the
air
separation
as
a prelimin
ary step.
Thm the
two-step
steam
and
air reforming
of hydrocarbons
became
the best
industrial
process of the hydrogen-nitrogen
mixture
preparing for more
than
60
y
ears
[4,5].
Assumingupproomately
the oxygen
and
nitrogen
content
in air as
20Vo and
80
0/o
respectively,
the
followingbasic
reactions of ammonia
production
from
natural
9s (CHa)
could
be
written:
3/8
CH{",+
:/a HzQgr
:318
CO,*,
+ 918 H:<er
- 77
.3
kJ (
1
)
3/8
CO(")
+ 3/8
1/8Or+
4/8Nr+
HzOrer:318
COzrel
+ 3/8 Hrr*l
+ 15 5
kJ
l/16CH1
:1116CO2+1/8H2O+
4/8Nr+
50.1k
J (3)
I2l8H2+
418
Nz: NHr
+ 462W
Summarising
reactions
(l), (2), (3) and (4), the total ammonia
production
process
could
be
expressed
by the
formal
reaction:
: sigcHa(e)*
5/8H2O(gr
+ 1/802
+ 4/8N2- NH{gr+
3.5/8COas)+
34
5 kJ (5)
Thus the
overall
heat of reactions
in ammonia
production
is slightly
positive.
But if water
enters
intotheprocess
as
a
liquid, the
overall
reaction
is
near
thermally
neutral:
3.5/8CHa(e)*
5/8H2O1rl
+ 1 l8O2+
4/8N2: NH:rer+
3 5/8cOz<er*
6.98
kJ (6)
The theoretical
minimum eners/ consumption
in natural gs-based production of ammonia
calculated
on
the basis
of the
reaCtions
(1)
- (6)
is shown
in
Table
1.
No heat
losses are
included.
3.
Energy
integration
in ammonia
plants
3.1.
Theoretical
and
actual
minimum
energy
consumption
in ammonia
production
-the model of
the chemical
processes, Inethodology
and
calculations
As was shown in section2,the overall heat of reactions
of methane-based
alrlmonia
production is
slightly
positive, i.e., a small
surplus
of heat e><rsts.
140
(2)
(4)
However,
this is a mere theoretical
thermochemical
calculation,
First I-aw-based,
using
the heat
quantities
only,
not
the
heat
pctential
(exerry).
As it is shown
in Table
l, the heat of the exothermic
reactions
(2) and
( ) is released at relatively
medium
and
low temperatures,
bu the
heat consumed
by
the endothermic
reaction
(1) must be
put
into the
process
at
very
high temperature.
which
can
be
only obtained
by burning
of some
kind of
fuel.
Thus two separate
treat
batances
must be
fitted:
a
high
temperature
(HT) heat balance
(Table2)
and a balance
of the
middle-
and
low-temperature
(MT<) heat
(Table 3).
Table
2 shows
that
the
balance
of the
higfr-temperature
heat
sources
and
sinks
is
not fitted.
The
heat
released
from the exothermic
reaction
of methane
burning
(3) by the
process air is nct sufficient
to
suppV
all
the
heat
necessary
for the
endothermic
steam
reforming
of methane
by reaction
(1).
Thus
an additional
quantity of medrane
must be bumt in ordet'
to fit the high temperaturc
heat
balance
of the process no matter
if the released
heat
is introduced
directly or indirectly
in the
steam
reforming
process. The problem
is where
this methane
could
be burnt without introducing
some
additional
nitrogen
into the
reaction
mixture. '
In the
commercial
ammonia
technolog,,
the
reastion
(1) is
partly
(W
to 50%)
going
simultaneously
withthe reaction
(3) in an autothermal
reactor
as
a second
step
(known as"secondary
reformind')
of the
hydrogen-nitrogen
mixture
generation
process
(Fig.
1)
The
first step
(steamieforming
oirnethane,
or "primary reforming")
is carried
out in a reactor
of
heat
exchanger
type,
heated
indirectly
either
by the hoieffluent
(ry to 10000C)
of the
second
step
autothermal
reactor or by combustion
of natural
gas
in a "reformingfurnace'. The
former
case
is
the
relatively
new
design
known
as
"gas-heated-reactor"
or GHR,
but
the
latter
is thetraditional
and
still
the
most common
design.
In this case
the
natural
gas
burned
in the
reforming
furnace,
is much
more
than
the
theoretical
quantity,
shown
in Table
1, calculated
to meet
the heat balance
of the
process. After the radiation
heat
transfer
in the furnace,
the remainder
flue gas
heat
is used
partly
for Hp steam
generation
and
superheating
and
then
for preheating
of the
process flows (natural
gas,
steam
and
air)
in the
convection
section.
The advantage
of the
GHR steam
reforming
design
is
the
elimination
of the
furnace
and
combustion
process,
but the major problem of the ammonia
plants with GHR is how to meet the higlr
iemperature
heat balance
of the
reformingand
of the
overall
ammonia
production
process.
Although
various
desrgns
are approved,
the common
approach
is the rejection
of the basic
principle of
modern
affrmonia
technolory to produce ammonia
using
stoichiometric
air quantity,
withod any
form of air separation.
The
most
med
approach
is to buin
the
additional
methane
using
surplus
of
air in the second
step autothermal
reforming
reactor
and obtain a non-stoichiometric
hydrogen-
nitrogen
mixture.
Then a new
problem arises
how to remove
the
surplus
nitrogen
from the
mixture'
The alternative
is to add
som. o"ygen
to the air,
but the air separation
is a highly energu
intensive
process.
As it is clear
from Table
2, the theoretical
minimum of energy
consumption
for the process
itself
(represented
by
LHV of methane)
i
s 22.2 GJltNHr, corresponding
to 620
Nm-' CHl/t
NH-r'
Not all real stage,
ol the modern
ammonia
technolory
are
included
in this model.
Nevertheless,
reactions
(l) - (6)
are
quite
enough
to present
the
ammonia
production
pro0ess'
The
methanation
reactions
of CO and
COz
are
combinations
of the
reverse
steam
reforming
(
1) and
CO conversion
(3) reactions,
hence
they are
included
in the model
indirectly The average
methane
concentration
in the
make-up
hydrogen-nitrogen
mi>dure
is 0.6-0
8o/o, cotrespondingto
about
4oA
of
the methane
feedstosk
entering
the steam
reforming As all this methane
is recovered
and
returns
back
to the reformingfurnac",
Urrt
as afuel, the overall
heat
balance
(Table
1) remains
unchanged
and
the total
methane
consumption
is nearly
the same,
only its distribution
between
feedstock
and
fuel is sligtrtly
changed.
neaity, the total methane
consumption
is sliglrtly higlrer,
as the higlr
temperature heat balance recluires
4% more heat to be put into the reforming furnace;
si-ultaneously
the
methanationreactions
(250-300t'C;
intt*se the
heat
supply
into the
medium
and
low temperature
heat balance.
Another
process,
included
indirectly
consuming
process.
The theoretical in the model, is the COz removal,
which is an enerry
minimum
separation
energy
consumption
depends
on the
t4l
concentrations of the
components
only.
Thus,
the
theoretical
(isothermal)
work
consumption
for
the
separation of an
ideal
mixture of CO2 and
hydrogeninitrogen
mixture
(known
as synthesis
or
make-
up gas),
based
on the stoichiometric
concentrations
of the
products
of the
reactions
(1), (2)
and
(3),
is included in the
theoretical
heat and
work balance of the
ammonia
production,
shown
in Table
1.
The real energ/ consumption
in separation
processes
is much
higher than
the theoretical
work
consumption.
However,
the exers/ consumption
is not so high,
because
in the most used
COz
separation
processes
the ener$/ input is as medium
or low temperature
heat. The actual
heat
consumption
for CO2 separation
in ammonia
plants
dropped
dramatically
in the last 30years from
about
5000 kJNm-'
to about
1200
-1400
lclNm''CO2.
Table I. Overall balance o/'exothermic
and endotherntic
heat o^/'reaction,s
in ammonia
prodttction
*Exerg,'
of mnsuned CH.r
(25"C.3
0 MPa)
Table 2. Theoretical high temperature ( , 8000C)
heat ltalance: availab le ancl
con,tutned heat o/'
reacrion.s
Production
process
Standard
hed of reactiou
(-aH,25"C.
I ol325
Pa) CHa consruned Average
reaction
tenrpem
-
ture. "C
Exergr,'
ofheat
G.l/t
NH,r
kJ/mol
procluct
of
reaction
k.T/r-nol
NHr (iJlt
NHr G.l/t
NH,
O,HV) Nrn'r/t
NHr
Exothermic reactions - available heat
Water
sas
shift reaction
(2) 41.t7 15.44 0.901 370-220 0.428
Methrure truming
reactlon
(3) 8t)2 34 5i).
l5 2 945 2 945 822 ri)00 2.255
Amnronia svnthesrs reaction
(4) 46.19 46. l9 2
112 425 1.554
Total heat frum ex oth ermic reac
tions I I
1.78 6.564 2.945 82.2 4.237
Endothermic reactions - consume(l heat
Steam refbrmins ofmethane (l) 206. I 0 7729 4.539 850 3.3 34
Water (
stoichiometnc) evaooration heat 44 01 21.51 1.615 235 0.668
Total heat for endothermic D
nocesses 104.80 6.154 4.002
Theoretical r,vork
consumption ftr CC)2
removal liorn H"AJ" mixture 2.84 0 167 0.167
Total heat and lvork consumntion 107.64 6.321 4.169
Suruhrs total 4. ld 0.243 0.068
Methane consumption as feedstoch
in
sfeam reforminq b1' reaction (l) 17.(t67 {93.3 18.595*
Total theoretical minimum methane
consumntion feedstoch and fuel) 20.612 5 /i.:r 21.690*
Production
process
Standard
heat of reaction
(-AH,
25"C,Iol325
Pa) CHa
consuned Averag c
reactlon
tempera-
tr-rre.
"C
Exergl'
ofheat
GJ/t
NHr
kJ/mol
product of
reaction
kJ/mol
NH-l G.I/t
NH,l G.Tit
NH3
(LH\D Nmrit
NI{:
Entloth ermic reactions - consumed heat
High temperaturrc heat consumption
Steam refbmrine
ofmethane bv reactton
(l) 206.10 77.29 4.539 850 3.334
Exothermic reactions - available he:rt
High temperature heat available
Methane buminq bl' reaction
(3) 8t)2
34 5i)
l5 2 945 2.945 822 I t)i)t) 2.255
Heat suppl.v
by atlditional methane
burnins 8t)2. 34 21 t4 I 594 I 594 44.5 l 000 t.221
Total heat sunulv bv methane burnins 802 34 77.29 d.539 4.539 126.7 1000 3.476
Surphrs total 0.0 0.0 0.142
Methane consumption as feetlstock in
steam reformins bv reacfion (l) r7.667 {93.3 18.595
*
Total theoretical minimum methane
consumution ffeedstock
and fuel) 22.206 620.0 23.367*
*Exerg' of musurred CHa
(25''C.
3 0 MPa)
r42
I\'lethan-
ation
i20"c
ffP s|esm I0 MPa 51d
4
'''L.*o,,,o,*,r,,,,,o.,,,,,,,,",
Heaf for waler prefreaf'ngr, sfeam geaeratron
, ,andsuperfteaffi ,
trig. L Flov;,sheet o/'an energ) integrated arnrnonia pro&rction plant
Table 3. Mediutn arul lov, ternperature 64f&LD heat halance: available and consunted heat
Production process
Standard
hed of reactiou
(-aH,
25"C. l ol325
Pa) CHa consuned Averag e
reaction
tempera-
ture. 'C
Exergy
ofheat
GJIt
NH3
k.Iimol
product
of
reaction
kJ/rnol
NH3 GJ/t
NH3 G.i/t NH3
GFrv) Nmr/t
NHj
Entlothermic Drooesses
- consumed heat
MT< heat consunqrtion in process
steam generation for reacfions:
o Stoichiometnc
tbr reactions
(l) and
(2)
o Escess
steam
(over stoichiometric)
Total forpmcess steam seneration
44 01
44 0I 27 51
t6 5i)
44.02
l 6l5
0.9(tc)
2.588
23 _5
235 t).668
t).401
1.069
Minimum actual
MI< heat consumptron
lbr CO" remor,'al
liom H'/lrtrr mirture t 1 1.1
I L. L.+ o 1t9 160 0 224
Total MT< heat cnnsumptim 56.25 3.307 1.293
Heat losses
l0% liom heat
surrplr 7 8l ()
459 i) 22t)
Total actual MT< heat conmmntion 6{.06 3.766 1.513
Erothermic reactions - available heat
Water gas
shift reaction (2) 4I tt 15
44 ().9Q7 370-220 0 428
Ammonia synthesis
reaction
(4) 46.19 46.t9 2.1t2 425 1.554
Total MT< heat
supply
frcm
erothermic
rreactions 61.63 3.619 1.982
Excess steam
condensation
heat 16.50 0.969 Itj- 6(\ 0.224
Total MT< heat suuulv 78.13 {.588 2.202
MT< heat su4rlus
for a.port steam
generation 14.07 0.822 0.689
Thus,
in Table 3 the value
1250 kJNm3CO2
is used,
plants
[a] The
preferable
temperature range
of the heat
as typ
ical in modern low
sources
is rdher narrow energy ammonla
for marry reasons,
t43
typically l7O-1400C.
hence.
the heat
available from the excess steam condensation
and other low
temperature
sources is used
mainly for this
purpose
In the
real
reformingprocess
not liquid
water,
but steam
is used as
a reagent in reactions
(1) and
(2)
Thus some heat is necessary
to evaporate
the water and this heat must be included
in the balance
[4]. Moreover,
the steam
reforming
of methane
by reactions
(1) and (2) requires
some surplus
of
steam
above
the stoichiometric ratio in order to obtain higlrer methane
and CO conversion
and to
prevent
carbon formation [4,5]. A 50to 100% surplus
is commonly used
with atrend towards
the
minimum of 50% surplus in newplants. Thus, thetotal heat necessary
for the water evaporation
is
about
2 6 GJIINH:. A part ofthe available middle- and low-temperature heat
from reactions
(2) and
(a) is consumed
to evaporate
the water for the process (Table 3). Indeed,
the heat consumed for the
evaporation
of the overstoichiometric
water is recovered back as the excess
steam is condensed in
the next stages
of theprocess. Brfr the exer$/ of this heat is much lower, because
the condensation
proceeds
at gradually decreasing
temperature from about 170t'down to ambient temperature
and
this heat
can't be
entirely
used. ,
It is clearthat
someheat losses
arepresent
in
all thermal
processes.
In themost common
design,
the
heat of the flue gas
released
into the atmosphere from the convection section
of the reforming
furnace,
is the maior source of the losses;
in the newest
GHR design these losses
are eliminated.
Some heat losses
through the insulation
and in the end coolers are unavoidable The industrial
practice
shows
that, depending
on the design. the heat losses
in modern ammonia
plants are
in the
interval l0-1soh, i.e.,
a thermal efficiency 85-90% could be reasonable. Assuming a minimum heat
losses
value equal
to 10o/o
of the exothermic reactions heat, this means
that 10% more methane has
to be burnt
to close the high temperature heat
balance"
Thus, the actual minimum energy consumptiur for the ammonia process itself could be
estimated as 22.7 GJlt NIIso corresponding
to 634 Nm' CHo/t NHi, including the minimum
feedstock (17 7 GJlt)
and
fuel (5.0
GJ/t) consunption,
respectively
(Table
4)
Table 1.
Acmal high tenrperature
( ,,,8000C)
heat balance;
at,ailaltle and con,sumetl heat oJ'
reacfiott.s
*Exerg'
of mnsunted
CHa
(25'C.
3.0
MPa)
Note:
ht utost
ammoniaplarts.
the h,pical
real methane
consum;ltion,
urarked
asfeedstod<
only, is r,'a1'
close
to the value
227 GJlt
[4].
Indeed.
this
value
nrcludes. except
the nrethane. convefted bv
reactiorl
(l),
also
the
nrethare
burned
in
the secondan' air
refomrins
bv
reaction
(3
).
Production process
Standard
hed of reactiou
(-aH.
2-5"C.
I0132,5
Pa) CHa consruned Arrerage
reaction
tempera
-
tr-rre.
"C
Exergv
ofheat
GJ/t
NHI
kJ/mol
product
of
rea ctlon
k.T/moI
NH-l G.I/t
NHr
G.l/t
NH-r
rLI{V)
Nm'/t
NHI
Endothermic reactions
- consume(l heat
Steiun relbmring
of nrethane
trr reacrion
(l) | :ClO. t0 | ll .Zrl I +.;.1,)
|850 I 3 334
Heat losses l0% liom heat
surrrrlr, 8.59 i) 504 85i) 0.3 7t)
Total hieh temperature
heat consumntion 8s.88 5.0{3 3.704
Exothermic reactions - available hea
High temperature heat available
Methane buming in the process bv reaction (3) 802.34 50. l5 2 945 2 945 82.2 I 000 2.255
Heat supply by additional
methane burning 802.34 27.t4 2.098 2.098 5 8.6 I 000 1.607
Total heat supply by methane burning 802.34 77.29 5.M3 5.&t3 140.8 1000 3.832
Su
rphrs total 0.0 0.0 0.128
Methane consumption as feedstoch in steam
rrformins bv reaction (1) r7.667 493.3 18.595*
Total minimum methane consumption
(feedstoch
and fuel) 22.710 63.t.1 23.902*
144
3.2.
Theoretical
and actual
energy
consumption
for shaft
work
generation
in ammonia
production
plants
In some references,
values about 22 GJ/t are specified
as the practical minimum methane
consumption
for ammonia
production,
in contrast
to the value
17 GJlt
(LHV of ammonia),
marked
as a
theoretical
minimum
[4].
However,
the
theoretical
(22
2 GJlt)
and
practical
(22.7
GJ/t)
minimum
eners/
consumption
values,
shown
in Tables
(2) and
(4), include the methane
consumed
in reactions
(1) - (6), if they are
performed
at atmospheric
pressure. Enerry
for the
reagents
compression
is not
taken
tnto
account.
As the
ammonia
synthesis
equilibrium
is unfavourable
at
low pressure and
the
deEee
of conversion
of the
hydrogen-n,trog"n
mixure to ammonia
is low even
at high
pressures, significant
additional
energ/
is required
to compress
the
hydrogen-nitrogen
mixture
(synthesis
gas)
to high
pressure
(8 -
:O Mpa), to drive
the recirculation
compressor
and also
to remove
alrunonia
from the unreacted
gaseous
mixture. '
Thus,thevalue
227 GJlt can't
be seen
as a
practical
minimum
eners/
consumption
measure.
In the
old
non-integated
and
multiple-trains
ammonia
plants,
designed
before
1965,
electric
motors
were used
to drive the reciprocating
compressors
used
at the time. In most modern
single-train
ener$/
integrated
ammonia
plants,
both make-up
synthesis
gas
and air compressors
are
driven
by
steam
turbines.
In plants designed
in the 60-ties
and
7O-ties
nearly
all pumps and
fans
are also
turbine
- driven The
corrplicated
HP (10- 14MPa)
steam
generation system
is
precisely fittedto
the chemical
processes in order
to use
most
effectively
the heat
of all reactions.
However,
as the
reactions
heat
is not sufficient,
significant
quantities
of fuel were burned
in these
plants for HP
steam
generation and superheating
The fuel consumption
depends
strongly
m the compressors
and turbines
efficiency
(Table 5,
Figure
Z) As th; efficiency of the first generation
high pressure
3 or 4 cases
centrifugal
compressors
was
rather
low,
ihe
steam
and,
accordingly,
the
fuel
consumption,
were
rather
high.
In
thesl plants
about
Zl3 ofthe natural
gas
was used
as
feedstock
and ll3 and
even
more
- as
fuel.
Auxlrary boilers
were
included
in ammonia
plants
in order
to generate
huge
quantities of HP steam'
about
5 to 7 times
the
produced ammonia
and
the total
natural
gas
consumption
was
about
40 GJlt
ammonia
. Anrnronia
plant,s
./i
om that epoch
are./hcetiously
de,scribed
amongst
pro./bs,sionals
as "a
steant
pou)et'plant,
r,hirh pt"odtrces
al,so
sotne
ammonia
as a by'ptroduct"[
4.
After lg73,the gowing enerry prices
pressure stimulated
the ener$/
saving
in ammonia
plants in
the next 20 y*ir, mainly b, reduction
of the fuel burning having as a result a total energy
consumption
drop
down
to 28
- 29 GJ/t.
Besides
the
substantially
improving
of the
technological
processes,
some
return
back
to the
electric
motors,
especially
for driving
pu-"pr and
fans,
"ont.ibrrted
slightly
to the enerry
saving
due
to the
low efficiency
of small
steam
turbines.
However,
in most
modern
plants both
compressors
are still
driven
by steam
turbines.
Various
options
were
tested
in last
20
y
ears:
to drive
the
air
compressor
by a
gas
turbine
or the
make-up
syngas
compressor
by an
electric
motor.
Some
attempts
are
made to
integrateammoniaand
CHP
powerplants
inthesamesiteby
shiftingthestperheatingtheHP
steam
(generated in
the
ammonia
plant)
to the
CHP
plant.
However,
last yea.r's
industrial
experience
shows no substantial
advantages
for any of these
versions.
It is il*r, that the situdion is changng
over the years due
to the improving
of the
compressors,
turbines,
as well as
the electricity
generation
in power plants
(Fig 2). Thm the
minimum eners/ consumption
point is gadually shifting
across
the parameters
space
roaming
between
electrical
motors
and
steam
turbines
driving
(Fig 2 - 4).
The steam
generation
system
strudure
and
the basic
steam
system
parameters
of all single-train
ammonia
plants
are
nearly
the same:
HP steam
10-14
MPa, stperheated
to 510
t 2O0C',MP
steam
extraction
for process
at
4-4.5
MPa [a].
Hence,
specifying
a set of basic
parameters of thetechnological
process,
it is
possible to calculate
the minimu* ,rul-ue of total feedstock
and
enerry
(heat
and
shaft
work) consunption,
then
to add
145
the values
of the heat and/or exers/ losses
and thus to approximate step by step the real
consumption
values. As a result
we obtain the real
values of the shaft
work, necessary
to drive
the
production
process
and
the
primary
ener$/
(methane)
consumed
for the
shaft work generation.
Then
the dependence
of the methane
consumption fbrshaft
work generation
on the basicparameters
can
be e><amined and
compared with the fuel consumption
in
a
power p
lant The
goal
of the comparison
is to specify
the set of
parameters
where
the steam turbine
drivers are
more
preferable
than electrrc
motors
and
vrce
versa.
To estimate
a minimum
of the shaft
work needed
for an ammonia
production plant,
at least
two
major
gas
compression
processes
have
to be taken
into consideration: compression of the
process
air from
atmospheric
pressure
to the
pressure
in
the
reforming
process,
which is
about
3 0
MPa,
and
compression
of the
purified
hydrogen-nitrogen
gaseous
mixture
(make-up
gas)
from the reforming
pressure
to the ammonia
synthesis
pressure,
which
in modern
plants
is specified in a rather
wide
interval
The lowest
value,
used
in commercial designs,
is 8.0 MPa,
the
highest
about
30 0MPa,
but
the most
used
in modern
designs are
synthesis
pressures
between
12to 22MPa, which
rQresent
a
flat
optimum
of total energy
consumption
[2] To explain
the exstence
of this optimum, two other
compression
proresses
have
also
to be considered: the circulation
(recycle)
compressor, and
the
refrigeration
compressor,
both
related
to the
ammonia
synthesis
section of the
plant.
The
shaft
work
consumption for refrigeration
and
circulation is much lower than
for the make-up
gas
compression
and depends conversely
onthe synthesis
pressure
Thus
thesum
of theshaft
work
consurption of
the
three compressors is nearly
constant
in
the optimum
pressures
interval112].
At the upper
limit of this interval,
the work, consumed
by the circulation and refrigeration
compressors,
is rather
low and only shaft work consumed
by the make-up
gas
and air compressors
could
be
included
in
the model.
Table 5. Sha.ftwork consut.rtpfion in arnrnonia
production plant,s
Process Sh aft lvorh
NH.,
GJ/t kWrft NHr
Theoretical shaft worli (isothermal) for driving:
. H:Nz coltlpressor 3 -20 MPa
o Air colnprcssor {).1-3 MPa
r Ammonia svnthesis recvcle
compressor
19-20
MPa
Total theoreticnl shaft lvorli generated
in steam turbines
o Refrigeration
conlpressor
. Others
(BFW plurlp.
COl renroval
solution
purlps. fars. etc.)
Total theoretical shaft lvorh (isothermal)
0.55
3
0.309
0.076
0.938
0
030
0 070
1.038
153.6
85 8
2tI
260.5
83
19 5
288.3
Minimum actual
shaftlvorl< (Ionn
:0.7) for drn,ing:
. H:A'{: collrpressor
3 20 MPa
o Air cornprcssor
0.
l-3 MPa
r Ammonia svnthesis circulation coulpressor
19-20 MPa
Total minimum actual shaft work generated
in steam turbines
r Refrigeration
compressor
. Others
(BFW punp, CO2
removal
solutiorl
prunps.
fars. dc.)
Total minimum actuarl
shaft lvork consumed
0 789
0 442
0 109
1.340
0.043
0.100
1.483
219.4
t22.6
3 0.3
372.3
I 1.9
27.8
412.0
Maximum actual
shaft work (r1i,or.,
:0.4) for
driving.
. H:N: colnpressor
31(l MPa
o Air compressor
0.l-3 MPa
r Ammonia
surthesis
circulation
colrlpressor
19-20
MPa
Total maximum
adual shaft work generated
in steam
turbines
r Refrigeration
compressor
. Others
(BFW
pulnp,
CO2
rernoval
solutbu
prunps.
fars. etc.)
Total
maximum
actual shaft rvod<
consumed
1.383
0.772
0 190
2.315
0 075
0.175
2.595
384.2
2t4.4
52 8
651.3
2 0.8
4 8.6
720.8
146
:o
E
(E
a 6.5
x(f,
,liI
cz A
ot
'+r- -)
$o
tr - 5q
fC
oo
oo-
ob c
6-6
F t 45
o
54
E
f,L ^-
J.C
045 0.5 055 06 0.65
Compressors
efficiency
(isothermal)
+,r,,+i;r*,r;,
1 PP n =0,28
2 PP
q
=Q,3
--'&.**.3
PP q
=0,32
---+* 4 PP q
=0,3
4
-t- 5 PP rl=
0,36
uzt/77722,6
PP q =0,3
8
+{'q 7-ST
-'tr*8-STactua,
I;ig. 2. Depenclatce
o.f the .fitel con,vunTttion
fur ,shcr.ft
v'rtrk genercrtion
ot? ilte e.fficiencr.,
o.f rhe mctin
cotnpres,ror,s
in crtltrlonia
plant,s crncl
,energr e.fficiatcl;o.f
Ttov,er
ltlant,s (PP) I- 6 - compressor,s.clriven
hr,,
electric ntotors; 7- I - cotn])re,r,snrs
clrit,eri
bt, ,rt'trr,rt
irb'iries (Si, ,tlecnn
senercttecl
m cmmonia plcrnt.
However, in all ener$/ integrated modern ammonia p lants, the circulation and make_up gs
compressors
are
fitted
together
and
driven
by a
joint driver
(steam
turbine).
The air compressor
is
driven
also
by a stea.m
turbine.
The refrigeration
compressor
and other machinery
(pumps,
fans,
etc.)
could
be driven
by small
steam
turbines
or by electric motors.
In most
modern plants
electric
motors
are
preferable
as drivers
of small
machines,
due to the relatively
low efficiency
of small
steam
turbines.
So, in this work the main
three
compressors
are
assumed
to be driven
bv steam
turbines,
other
machinery
- by electric
motors.
The isothermal
shaft work values
shown in Table 5, represent
the theoretical
minimum
work
necessary
to run the ammonia
synthesis
reaction
at 20 MPa. In order
to have
actual
values,
the
efficiency
of the compressors
should
be known. In Tables
5 and 8 two examples
are shown,
representing
the minimum and maximum
actual
shaft work consumed
by the compressors
at
boundary
values
of the isothermal
efficiency (0
7 and
0.4,
respectively).
Forthe first example,
the
heat
balances
and
overall
methane
consumptron
in ammonia
plants
*ittr steam-turbines
driven
and
with electric
motors-driven
main
compressors
are
shown in Tables
6 and7, respectively.
A comparison
of the fuel (methane)
consumption
for shaft
work generation
in ammonia plants
(without
and with heat
losses
in
the
steam
system)
and
in power
plants
(First
l,aw
efficiencies
from
0
28
to 0.38)
at
isothermal
efficiencies
of the main
compressors
from
0.4
to 0.7,
is
shown
in Figure
2. The
dependence
of the fuel (methane)
consumption
for shaft
work generation
on
the
efficiency
of
the
compressors
in ammonia
plants
and
energz
efficiency
of power
plants
is shown
in Figure
3 The
t47
Figure
4 presents
the influence
of the heat losses
in the steam
generation
system of ammonia
plants
over
the fuel (methane)
consumption for shaft work generation.
The results
show that the fuel consumption values for the shaft work generation
in ammonia
and
powerplants are comparable
and depends strongly
on the machinery
efficiency
in ammonia
plants
and on the energy efficiency of power plants,
respectively.
Due tothe utilization of apart of the
available MT< heat
from the chemical
processes
in the steam cycle, the fuel consumption
for the
work generation in ammonia plants is lower than in power plants working at equal steam
parameters.
Table 6. Heat and
^/ilel (methane) con.sumption./br
,sha.li
u,ork
getterafictn
in amrnonia
production
(A4ain
com
pre,tror'.r
clril,en by .\ team nrrbine,s
)
Process Shaft
worh
GTh
NH.
Steam
kg/t NH3
CHa conzumed Exergy
of lvork
or heat
GJ/t NHl
Exergv
of CI-Ia
GJ/t NH3
LHV GJ/t
NH3 Nm3/t
NH3
Shaft wod( to be
generatedin
ammoni:r
nlnnt- main comt)nessoru
driren bv steam
turbines
Total minimum actual theoretical shaft lvork
generated in steam furbines l4:0.7
' FP steam
ll0 MPa. 50Cf'C)
to MP $earn 4MPa
' IvIP steam 14
MPa) to condensation
Total shaft lvorh generated
().422
0
9l8
1.340
2244
I 183 0.422
t)
9I8
1.340
Heat
consumntion
for HP steam senemtion
in arnm onratil arnt
Heat consum;ltion for HP steam generation:
. Stearn superheating
o Water evaporation
. tsF \\'ater
preheating
Total heat for HP steam generation
I 458
2 953
2 857
7.268
:/++
0
759
t 372
0 854
2.985
Actual me
tfum an tl loll' tem
rrcrzrtu
rt (MT&L T) h eat ba an oe
Total MT< heat availablefmm reactions (2)
and (4) 3.619 1.982
Excess steam condensation
heat 0.969 c\ 220
Total MT< heat sunnlv 4.588 2.202
Minimum actual MI&U| heat consumotion fbr
CC). removal liom H"A.J. mixture (\.7
t9 0.224
Heat losses
(10% fiorri heat
surrrrll') 0.459 (\ 22(l
MT< heat availablefor BFrvater preheating
and rvater evaporation 3.410 1.758
Hish temrrcmturc
(HT)heat balanoe
HT heat consumption tbr HP stearn
generation:
o Steam superheating
o Water evaooration I .458
2 4t)0 2244 I .458
2.400 40.l
(t7.0 0.159
l.i)4t) l 534
3ll0
Total HT heat consume(l forHP steam seneration 3.858 221t 3.858 107.7 r.799 4.060
Heat
losses
(10% fiom methane bumms heat) C\
42C) 0.429 12 t) 0 452
Total HT heat suppl.v bv atlclitional methane
burnins 4.287 1.287 119.7 t.799 4.512
Total
actual
minimum methane
consr
m
Dtion
in immonia pl
ant
Actual minimum
methane
consumption as
feerbtocli
and fuel for lrroaess
(from Table 4) 22.711 634.1 23.902
Total
actual
minimum methane
consum;ltion
for HP steam
generartion 1.287 r19.7 1.799 4.512
Total
actual
minimum methane
consumption
in ammonia
plant 26 998 753.8 28.415
Electricity
from
power plant
for driving other
rnachinen' 0 143 0 143
Fuel
(mdhare) consunption in po\\erplant for
electricrtl' generdion (r1:0.3
2) 0.447 t2.5 0.472
Totarl
erctual
minimum meth2rne
con sum
ption
in ammonia rrlant find. electricitv sener:rtion) 27.145 766.3 28.886
148
Table 7. Total rnethane
coltsurnplron
in ammonia plant and ./br elecf iciqt production in pov,
er plant
(All compre,t,tot".s
in arnrnonia plant clriven b.1t electric motor,s)
Process Shafi
rvork
G.l/r
NH3
CHa consruned Exergi'
of CHa
GJ/t NHI
I-HV
GJ/t NH. Nm'/t
NH.
Actual
minimum methane
consumption
as feedstodr
and
fuel for prooess (from Table .l) 22.711 634.1 23
902
Minimun elrctricity
from po\4er
plant
for driving
all
machinen' 1
483
Minirnun fuel (methane)
consrunption m
po\\er
plart for
electricitl'
generdion
(q:0.3
2 l4l) 4 634 t29 4 4 877
Total minimum methane
consumption
in ilnmonia and
porver Iilants 27
315 763.5 28.779
Maxitnrun electricit.v
from po\\€r plant for driving all
machinery 2 595
Maxinrrurr
fuel
(methare)
consunptiorr rn
po\\€r
plant
for
electricrtv
generdion
(q:0 32 l4l) 8 109 226 4 8 534
Total maximum methirne
consumlltion in iunmonia and
t)ower Dlants 30.820 ti60.s 32.136
Table
B. Theoretical and acfttal energg)
consumpfion
and CO
2
enti,gsion,s in nafitral ga,s-ba,sed
production of' amrn onia
Methane
consunption ard CO2 emissions
in arrmonia
product
ion plarts Methane
consurrption CO3
emissions
ky t NI{3
GJ/t
NH. Nm-'/t
NH.
111 lll lll ax rnin max mlll Max
Methane
as
feed$ock
for $eam reformingreaction
(l) t7.667 493
3969
Methane
buming reaction
(3) 2 945 822 r62
Addit
ional
m
dhare bum
iu
s l -594 445 87
Theorctical
minimum
consumption for dremical
l)rooe
ss 22.2M1 620.0 1218
Heat
losses
in methare
brnring
(
lt)%) 0 -5t)5 14l 28
Actual
minimum
consumDtion
for chemical
Drccess 22.711 63.t.1 r216
Act
o
a
ral consumption for worli generation:
ll amulonia
plants
n po\ter plarts
4.287
0.447 8 031
0 78r It9 7
t25 224 2
21.8 2t2
24 440
43
Total
actual
consumption in BATnerv
plants:
Main compresson
driven by steam turbines 27.14531523 766.3 880.1 1505 1729
Totarl
actual consumption
in BATnerv plants:
All machinery
driven by electric
motors 27 34s30.820763.5 860.s 1500 1690
CO2
ben drm
arh allowan
ces
fo
r amm oni a produ
ction
for 201 s-.7,014;
carbon
leakage
eriposure
is in
considerdion
@C
Decision
27
.4.201l,
[3]) 29 522 824.2 t6t9
CO2
ben chm arl<
allolyan
ces
for iunmoni
a prorfu
ction
for2020 if cmbon lealiage
exposure uould
be
not in
considerdion
(factor
0.8
for 2013
dorur to 0.3
for 2t)20) ll07l 309 l 607.1
149
8
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
l<
lr
o
3
*.,
lF
(E
o
lr
e
.9
{rr
CL
E
f
o
o
()
o
q
(E
+,
o
E
(v)
I
z
+,
f
o
c
o
+r
(!
L
o
o
clt 0.6
x
I or pressors
efficien
cL
{
isothermal
)
- Electricity production efficiency of power plants
ll.
Fig. 3. Dependen
ce of' the.fu
el (m
ethan
e) consumption
./br ,sha"ft
v)ork generatiotl on the
e./Jiciency
q/'the compt'es,t'or,t'
in amrnonia
plant,t ancl enersg)
e./liciencl,
o7'1rort,er plan t,t.
-Y
l-
o
=
+,
Its
(U
o
r- Cv)
€-
cz
o<
o' g)
tr
=c
6o
c.5
of!
o6
96
kcD
*.,
o
E
=
o
5
lJ.
I
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
G om
p
ress
o
rs eff
i c i en c,1r
J[?"tJi]3#fll, o niu
pra
nt,
yo
Fig. 1.
Dependence
of the.fuel (methane)
con,tumption.for,shaJiv)ork
generarion
on the
efliciency
o.f
the compre,tsors
and heat
los,se,s in antmonia
plants.
t -50
3.3.
Theoretical
and
actual
minimum
CO2
emissions
estimation
The proposed
model of the ammonia
production
process
enables
specifying
separately
also
the
theoretical
and actual
CO: emissions
from the chemical
process
itself
and
from the shaft
work
generation.
The
first conclusion
is that
the
COz
emissions
couldn't
be
made
lower
than
1218
kg/t,
"o.r"rponding
to the
theoretical
minimum
methane
consumption
for the
chemical
process
(Table 8)'
Moreover,
extra
emissions
must
be
added
from the
shaft
work generation
processes
in the
ammonia
plant
or in a power
plant. In case
the main compressors
are
driven
by steam
turbines
(HP steam
generated
in the
ammonia
plant), the COz
emissions
would
be
in the range
from 236
to 483
kg/t,
iependingon
the
turbines
and
conpr"rroi, efficiency.
In this casethetotal
actual
minimum
of the
COz
emissions
would
be
from I482to 1729
kg/t
(Table
8) In casethe
main
compressors
are
driven
by electric
motors,
thetotal actual
minimum
of the COz
emissions
would be from 1500to 1690
kgit, depending
on
the power
p
lant efficiency.
The comparison
of these
values
with the COz
benchmark
allowances
for ammonia
prpduction,
establish.A
Uv
the
European
Commission
[13]
foryears
2012
and
2013,
shows
thm
the
value
1619
kg/t is within the range of the actual
minimum
values
for both shaft
work generation
options'
The
fulfilment
of this regulation
requires
the
application
of the
best
available
ammonia
technology
as
well
as
the
high
efficient
compressors
and
turbines.
However,
if the proposed
in the same
EC decision
[13] further
CO2
emissions
reduction
(linear
decrease
by factoi
of o"g
for z0l3 down
to 0.3
for 2020)
would
be implemented
for ammonia
plants
as
well, the
corresponding
value
of 607 ky't would
be
unfeasible
since
it would
be
twice
lower
even
than
the
theoretical
minimum
of 1218
kg/t
for
the
chemical
process only.
4.CONCLUSIONS
. A simplified, but generaltzed
model of the overall ammonia production process,
presented
by
reastions
(1) - (a), is usedto distinguish
the methane
consunption forthe chemical
process and
for the eners/ transformation pror"ir.s (shaft work generation).
The model is applicable
to all
types of modern ammonia plants with conventional
reforming advanced reforming and gas-
heated
reforming as the model parameters
for methane
consumption and heat balance
of the
plant are
rndependent
from the features
of the specific
plant design.
The model is used
to find the
theoretical
minimum and actual methane "onrr-ption of the chemical
processes
in ammonia
production.
The dependence
of the actual
consumption
on the heat
losses
is e>camined.
. The dependence
of the additional fuel consumption for shaft work generation
in ammonia plants
on the isothermal
efficiency of the compr.rroi, and
thermal
efficiency of the steam
generation
is
investigated
and compared with the fuel consumption in power plants with different enersi
efficienci
es.
. The results
show
that the fuel consunption values
for the shaft
work generation
in ammonia
and
power plants are comparable and depends strongly on the machinery efficiency in ammonia
plants and on the energr efficiency of power plants, respectively.
Due to the utilization of a part
of the available MT< heat from the chemical proresses in the steam cycle, the fuel
consumption
for the work generation
in ammonia
plants
is lower
than in powerplants workingat
equal
steam
Parameters.
. At higher machinery and thermal efficiencies,
the generation
of the shaft work in the ammonia
planis itself
is prefe.able
than in old power plants withtypically lower efficiencies.
However, as
the power plants offer more opportunities
for improvements
than ammonia
plants, in the ftfrure
electric
motors could become agtrnpreferable
for compressors
driving
. The
theoretical
and
the actual
minimum of the COz
emissions
from the chemical
process
itself and
from the shaft work generation are specified and compared for both cases of the main
compressors
drivers.
steam
turbines
and
electric
motors'
l-51
Nomenclature
BIrW Boiler
Feed
Wder
CHP Combined Hed ard
Pouer
GHR Gas-Heated Refomring
HP High Prcssure.
MPa
HH[,' High Heating
Value.
kJ
LHL. Lorv
Heating
Value.
kJ
LP
LT' Low-Pressure.
MPa
Lou'temperatrre-
"C
MP Middle Pressure.
MPa
MT M iddle T
emp erd ure.
'
'C
tt efficiencv
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2OI2
The 2\*.'Intern:rtional
Conferenc:e on Efiic:iency,
Cost,
C)ptimizatton
and Simulation of Eneruy Conversion '
Systerns
and
Processes
(Perugia,
June
2(,'r'
-lnne
)9'h,
2(:)12)
eclitecl
by
UiMennr<t DEsroERr,
C}tAMpAor-<l
MANFRTDA.
F,rvnrco
S<-rrrBBn
FIR I]NZE LINIVERSITY PR ESS
2()I2
ECIL)S
l0 l2 : the 25'i'
lntern:rrir'rnal
Clitnterelr(re
olt Etlicrerr,:r..
Closc.
OFtrnrtzrltlon
lnd Sr rnulattctn
oI F.nergt Clr)r]\.erstLrll
S1'stenrs
an.l Processes
(Pelugr:r,
_June
26'f'-_June
29'r',. 20i2) /
edite.l Lry
Unrberto Desiden. CliarlF:rolo Mirnti-idr. Enrrco
SciuL;Lra.
Firenze: Firenze
Unrversicv
Press, 2(112.
(Proceeclinus
e report l9(.))
hrtp: //cligi
rel.
c;rsah ni.irl97888 6
rr55322
q
ISBN q78-88-6655-322-q
(onlrne)
Prr:;letto
grrrflco
dr copertrnir
Alberto Przarro. P:rgina
Maestra snc
Irnrnagine cli copelttna: (.lj
Kts ] Drearnstirnle.conl
Pccr Rrt'icll Pr,r,:.s-t
All ;.u[]1.-",1ons
rlre
subrrrittecl
lLr an e-\ten)ll letbreeing
pro.ess un.ler the responsibrlrt), ot'the FUP
Edicorral Boarcl ancl the Sciencrflc
Clorrrniittees
of tfreinclrvrclual
series.
The u'orks
puLrlrsheci
in che
FUP catalogttr:
are evlluittec-l
ancl
aFproved Ltl' the Fdrrorial Board oI the publlrhrng house. For ir
tnore tle!:riled
rlescrrpcion
ot'rl're
retbreerng
pro.ess
r.ve
reti.r
ro rhe otllcial .locumenrs puLrlished
on
the u'ebsite:rn.i
rn che online catalogue
ot'the FUI) (htr;.://11'1a'.0'.tirprg5r...-)mr.
Fi rcrr.-c
{irtit'tr:tt1,
Prt'-r-i Erlir,rri,r
I Boarrl
Ci. Nrglo (C)o-ordrn:rtot).M
T Bartoli. M. Bo.-i.lr. F. C]inrl,r.
R. C}salbuonr.
(1.
Cli:r;.;.er. R. Del Puntl.
A. Dolfl. \'-.
Fart{ron, S. Ferlone.
M. Cl:rrzrrnicr.
P. Clur'rrnren.
Cl. Marr.
M. Marrnr. M. \-erca.
A. Zorzr.
i.r
2012 Firenze Unrr,ersrtv
Press
Urrrversrtii
.leslr StLr,li
di Frrenze
Ilr
renzr: Ljrr
rversr tt, Press
Bt)rst) .\lLrrzr.
28. 50lar Frlcrnze.
Irllv
h ttp
://u"'vu'. fir press.
cor n
/
Printrd irt Ital1,
Advisory
Com
m ittee
(Track
Organizers)
Building, Urban and Complex Energy Sysfems
V.
lsmet
Ugursal
Dalhousie University, Nova
Scotia, Canada
Combustion,
Chemical Reactors,
Carbon Capture and
Sequestration
Giuseppe Girardi
EN
EA-Casaccia,
ltaly
Energy Sysfems
: Envi ron mental
and Sustainability /ssues
Ch
ristos
A. Frangopou los
National Technical
University
of Athens, Greece
Exergy Analysis
and Second
Law Analysis
Silvio
de Oliveira
Junior
Polytechnical University of Sao Paulo, Sao Paulo,
Brazil
Fluid Dynamics and Power
Plant Componenfs
Sotirios Karellas
National
Technical University of Athens, Athens,
Greece
Fuel Cells
Umberto Desideri
University
of Perugia, Perugia,
ltaly
Heat and Mass Transfer
Francesco Asdru bali, Ci
nzia Buratti
University
of
Perugia, Perugia,
ltaly
lndustrial Ecology
Stefan
Goessl i n
g
-Rei
seman
n
University of Bremen, Germany
Poster Session
Enrico Sciubba
University
Roma 1
"Sapienza",
ltaly
Process lntegration and Heat
Exchanger Networks
Francois
Marechal
EPFL,
Lausanne, Switzerland
Re newa ble Energy Co nve
rsio
n Sysfems
David Ch iaramonti
University
of
Firenze, Firenze,
ltaly
Simulation of Energy Conversion
Sysfems
Marcin Liszka
Polytechnica Slaska, Gliwice,
Poland
Sysfem Operation, Control,
Diagnosis
and
Prognosis
Vittorio Verda
Politecnico di Torino,
ltaly
Thermodynamics
A. Ozer Arnas
United States
Military Academy at
West Point, U.S.A.
Thermo-Economic
Analysis and Optimisation
Andrea Lazzaretto
University
of Padova, Padova,
ltaly
Water Desalination and Use of Water Resources
Corrado Sommariva
ILF
Consulting M.E., U.K
iii
Scientific
Committee
Riccardo
Basosi,
University
of Siena,
ltaly
Gino
Bella,
University
of Roma
Tor
Vergata,
ltaly
Asfaw
Beyene,
san Diego
state
University,
United
states
Ryszard
Bialecki,
Silesian
lnstitute
of
Tecnology,
poland
Gianni
Bidini,
University
of
perugia,
ltaly
Ana
M.
Blanco-Marigofta,
University
of Las
Palnas
de
Gran Canaria,
Spain
olav
Bolland,
University
of
science
and
rechnology
(NTNU),
Nonrvay
Rene
cornelissen,
cornelissen
consurting,
The
Netherlands
Franco
Cotana,
University
of
perugia,
ltaly
Alexandru
Dobrovicescu,
Polytechnical
University
of Bucharest,
Romania
Gheorghe
Dumitrascu,
Technical
University
of
lasi,
Ronnnia
Brian
Elnegaard,
Technical
University
of
Denrnrk
, Dennnrk
Daniel
Favrat,
EPFL,
Switzerland
Michel
Feidt,
ENSEM
- LEMTA
University
Henri
poincar6,
France
Daniele
Fiaschi,
University
of
Florence,
ltaly
Marco
Frey,
Scuola
Superiore
S.
Anna,
ltaly
Richard
A Gaggioli,
Marquette
University,
USA
Carlo
N.
Grinaldi,
University
of
perugia,
ltaly
Sinnn
Harvey,
Chalrners
University
of
Technology,
Sweden
Hasan
Heperkan,
Yildiz
Technical
University,
Turkey
Abel
Abel
Hernandez-Guerrero,
University
of
Guanajuato,
Mexico
Jiri
Jaronir
KlenBS,
University
of
pannonia,
Hungary
Zornita
V. Kirova-Yordanova,
University
"prof.
Assen
Zlatarov",
Bulgaria
Noam
Lior,
University
of Pennsylvania,
United
States
Francesco
Martelli,
University
of Florence,
ltaly
Aristide
Massardo,
University
of
Genova,
ltaly
Jim
McGovern,
Dublin
Institute
of Technology,
lreland
Alberto
Mirandola,
University
of Padova,
ltaly
Michael
J. Moran,
The
ohio state
University,
united
states
Tatiana
Morosuk,
Technical
University
of Berlin,
Gerrnany
Pericles
Pilidis,
University
of
Cranfield,
United
Kingdom
Constantine
D. Rakopoulos,
National
Technical
University
of Athens,
Greece
Predrag
Raskovic,
University
of Nis,
serbria
and
Montenegro
Mauro
Reini,
University
of Trieste,
ltaly
Gianfranco
Rizo,
University
of Salerno,
ltaly
Marc
A.
Rosen,
University
of
Ontario,
Canada
Luis
M. Serra,
University
of Zaragoza,
Spain
Gordana
stefanovic,
university
of Nis,
serbia
and
Montenegro
Andrea
Toffolo,
Lule6
University
of
Technology,
Sweden
Wojciech
Stanek,
Silesian
University
of Technology,
poland
George
Tsatsaronis,
Technical
University
Berlin,
Gernrany
Antonio
Valero,
University
of Zarago:za,
Spain
Michael
R. von
Spakovsky,
Virginia
Tech,
USA
Stefano
Ubeilini,
Pafthenope
University
of Naples,
ltaly
Sergio
Ulgiati,
Parthenope
University
of Naples,
ltaly
Sergio
Uson,
Universidad
de
Zaragoa,
Spain
Rormn
Weber,
Clausthal
University
of
Technology,
Gerrnny
Ryohei
Yokoyama,
Osaka
Prefecture
University,
Japan
Na
Zhang,
Institute
of
Engineering
Thernnphysics,
Chinese Acadenry
of Sciences,
China
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