FVO Nr.
3123
Fabrieksvoorontwerp
Departement of Chemical Technology
Subject:
Removal of S02 and NOx from flue gas
from an electric power plant using
Interconnected Fluidized Beds
Authors:
F. van der Ham
G. van Oosterbaan
N.H.A. Versloot
Torellistraat 39
Moriaanseweg West 34
de Noordbank 32
3222 AD Hellevoetsluis 3181 MH Rozenburg
01883-12201
01819-18215
,
f!,!f(
Date assignment
Date report
3208 NE Spijkenisse
01880-33809
October, 31 1994
February, 10 1995
Removal of S02 and NO
x
from fiue gas
from an electric power plant using
Preface
To remove S02 and NOx from flue gas from an electric power plant several methods are available. The NOXSO process is based on adsorption to followed by regeneration from a sorbent with pneumatic transport of the sorbent to the different stages. As an alternative, in this Prelirninary Design Assignment (pDA; in dutch: 'FVO') reactions and transport take place via an Intercolll1ected Fluidized Bed System (IFB). The design will be based on the NOXSO process, i.e. using the same process conditions.
In writing this report, we wish to thank a number of people in supporting us and pro vi ding us with information. First of all, we thank Ir. O. C. Snip for supporting us through the whole project. Mr. M. Woods, Sr. Project Engineer at the NOXSO Corporation, provided us with much of the information needed in designing the reactors. Finally, we wish to thank Ir. C.P. Luteijn for giving us the opportunity to have this subject as a PDA and for his contribution to the design ofthe regenerator recycle.
Delft, February 1995 Frank van der Ham Gerard van Oosterbaan Nico Versloot
Summary
The NOXSO flue gas desulfurization process is operated as an Interconnected Fluidized Bed system. Five fluidized beds are used as Adsorber, Heater, Regenerator and Coolers respectively. Three beds are used as transport beds. 172.28 Nm3/s offlue gas (from a 150 Mwe power plant) is fed to an adsorber, in which 90% ofthe NOx and 95% ofthe S02 is
removed. The module pro duces 16,449 ton sulfur per year. Total yearly costs are 85.5 M$.
Operating the NOXSO process in a Interconnected Fluidized Bed system is more expensive than the original process. Major disadvantage is the fact that all reactors must be single stage reactors. The original NOXSO process is multi-stage operated. Especially the heater in the IFB system is inefficient compared to the NOXSO heater. The NOXSO heater is operated in a multi-stage, countercurrent way, which is more efficient. This implies more natural gas consumption, which is a large cost factor for the total process.
The design ofthe regenerator was complicated due to the fact that regeneration reactions (and kinetics) are not available. More reliable results can be expected when these are present. The NOXSO Corporation is still doing research on this subject.
Contents
Chapter 1 Introduction
1
Chapter 2 Background and objectives
2
2.1 Flue gas desulfurization: the NOXSO process 2
2.1.1 Raw flue gas properties 2
2.1.2 Sorbent properties 3
2.1.3 Adsorption chemistry 3
2.1.4 Sulfur regeneration chemistry 4
2.l.5 Nitrogen oxide regeneration 4
2.2 The objectives 4
2.3 Physical properties 4
Chapter 3 Process structure and process flowsheet
6
3.1 The NOXSO process operated with Interconnected Fluid Beds 6
3.2 Adsorber 7
3.3 Heater 3.4 Regenerator 3.5 Cooler
Chapter 4 Calculation of the equipment
Chapter 5 Mass and energy balances
Chapter 6 Equipment list and specification forms
Chapter 7 Process control
Chapter 8 Safety, health and environmental aspects
8.1 HAZOP study 8.2 Safety 8.3 Health 8.4 Environmental aspects10
11 1215
19
29
32
33
33 3334
34
Chapter 9 Economical aspects
9.1 Process costs 9.l.1 Variabie costs 9.l.2 Labour costs 9.l.3 Investment costs 9.2 Return On Investment 9.3 Internal Rate of Return 9.4 Cost evaluationChapter 10 Conclusions and recommendations
List of used symbols and abbreviations
References
35
35
35 35 3638
39 3940
41
44
1
Introduction
Combustion of coal or any other organic fuel produces a lot of - at first - unuseful
byproducts, like ash, S02' NOx. These components ofthe flue gas turn out to be the main problem concerning acid rain. Results of this phenomenon can weU be seen in Western Europe when looking for a nice Christmas tree ...
This led to some sort of consensus about the idea of removing S02 and NOx from the flue gas of electric power plants. Science and technology have to deliver the answers to many questions. The question which wiU be dealt with in this Prelirninary Design Assignment (PDA) is: 'WiU the applying ofInterconnected Fluidized Beds be useful in the removal of S02 and NOx?' Thus a major point oftechnology. Background ofthis idea is the (pilot plant scale) design ofthe NOXSO Corporation, using fluidized beds together with
pneumatic transport of sorbent partic1es. Disadvantage ofthis type of transport wiU be the large effect of attrition ofthe partic1es. Both processes (further caUed 'NOXSO process' versus 'IFB proces') have the same principles: adsorbing S02 and NOx on a sorbent and regeneration of the sorbent (together with the removal of S02 and NOJ. Only S02 will lead to a useful product after leading it to a sulfur plant: high grade sulfur, sulfuric acid or liquified S02 can be valueable products.
The scope ofthis PDA wiU therefore be the use of an IFB system to remove S02 and NOx from flue gas of a 150 MW e electric power plant. Research on a comparable process is done at the Delft University of Technology.
2
Background and objectives
2.1 Flue gas desulfurization: the NOXSO process
The patented NOXSO process employs regenerabie, dry adsorption to remove over 95%
of sulfur dioxide and nitrogen oxides ±fom boiler flue gas.
Flue gas ±fom the combustion process flows upwards through a fluidized bed of sorbent
beads. S02 and NOx are adsorbed ±fom the flue gas on the surf ace ofthe sorbent. Once
loaded the sorbent is transferred to a sorbent heater to begin the regeneration cycle. In the heater, nitrogen oxides are stripped ±fom the sorbent with air and returned as combustion
air back into the burners ofthe furnace to be reduced to nitrogen and oxygen.
The hot sorbent is then transported to the regenerator, where the adsorbed sulfur compounds are removed in a series of chemical reactions. Gases produced in the regenerator are send to an off-gas processor where either commercial grade sulfur, sulfuric acid or liquid S02 are recovered for sale. The cleaned sorbent is th en cooled in a fluid bed, and returned to the adsorber for reu se.
Clean Flue gas NOx to burner H2S/S02 10 sulfur plant
/1' /1' /1'
S orbenl
~
,
"
" Adsorber Heater / Regenerator Cooler /
/1"
Raw Flue gas
Figure 2.1: NOXSO regenerative desulfurization process
2.1.1 Raw flue
gas
properties
The raw flue gas properties based on an open loop system (no recycle ofregenerated NOx
2 Background and objectives
172.28 2400
500
2.1.2 Sorbent properties
The sorbent is prepared by spraying N~e
(incipient wetness procedure) and th en it
03 solution on the surface of y-alurnina spheres is subsequently air dried. The properties of the sorbent are listed in table 2.2.
Porosit
2.1.3 Adsorption chemistry
The active sites on the sorbent are sodium sorbent's capacity to adsorb S02 and NOx during the adsorption process are the follo S02
+
Al(1) -+ Al·S02 . NO+
Al(2) -+ Al·NO N02+
Al(3) -+ Al·N02 Al·NO+
S02+
0.5 02 -+ Al·S02+
N02 S02+
N~O(1)+
0.5 02 -+ N~S04 5.2 250 . 1000 3.8 1200 0.65and alumina, wruch both contribute to the from flue gas. The main reactions taking place wmg : (2.1) (2.2) (2.3) (2.4) (2.5) ~S04 + NaN03 S02
+
NO+
1.5 N~0(1)+
1.25 02 -+ N S02+
NO+
N~O+
02 -+ N~S04+
NO 2 (2.6) (2.7) 3 N02+
N~0(2) -+ 2 NaN03+
NO 2 NaN03+
S02 -+ N~S04+
2 N02 Temperature in the adsorber is 120 oe (39(2.8) (2.9) 3 K).
2 Background and objectives
2.1.4 Sulfur regeneration chemistry
Much research is done in getting a sufficient reaction model for the regenerator. Until now, some overall reactions have been proposed, according to Yeh et al. [Ref. 3]:
4 N~S04
+
CH4-+
4 N~S03+
CO2+
2 ~O4 N~S03
+
3 CH4-+
4 N~S+
3 CO2+
6 ~OAl20 3
+
N~S03<=>
2 NaAl02+
S02 Al20 3+
N~S+
~O<=>
2 NaAl02+
~SNatural gas is used as reducing gas.
Temperature in the regenerator is 620 °C (893 K).
2.1.5 Nitrogen oxide regeneration
(2.10)
(2.11)
(2.12)
(2.13)
NOl( desorbes from the sorbent in the heater. Heating is do ne using air as heating medium. The air coming from the heater (with desorbed NOJ is used as combustion air in the coal fumace. Inside the fumace, NOl( is reduced to nitrogen and oxygen.
2.2 The objectives
The objective ofthis PDA is to design an IFB system for the 95% removal of S02 and
90% removal of NOl( from flue gas from a 150 MWe electric power plant. The process conditions (especially the temperatures) wi11 be based on data from the NOXSO process.
2.3 Physical properties
Table 2.3 summarizes some important physical properties ofthe components in this process. They are listed from the lowest boiling point up to the highest. Table 2.4 shows the MAC values and the properties which determine the explosion hazards of a few of the components. These properties are:
AlT: Auto Ignition Temperature MIE: Minimal Ignition Energy ELair: Explosion Limits in air
2 Background and objectives -82.5 4 4 30.01 -15l.8 -94.0 65.8 34.08 -60.7 100.4 90.1 64.06 -10.0 157.2 78.7 46.01 2l.2 18.02 100.0 374.2 22l.2 2 25 2 260 0.07 4.0 - 46 4
3
Process structure and process flowsheet
3.1 The NOXSO process operated with Interconnected Fluidized Beds
Removal of S02 and NOx from flue gas is done by a combination offluidized beds within
an Interconnected Fluidized Bed system (IFB). See figures 3.1 and 3.2.
The IFB system consists of eight fluidized beds: four lean beds (high voidage) and four dense beds (low voidage). Each lean bed is followed by a dense bed and vice versa.
Particles flow from a lean bed over a weir to a dense bed. From the dense bed the particles
flow to the next fluidized bed through an orifice.
1 2 3 4 5 6 7 8
lean bed dense bed lean bed dense bed lean bed dense bed lean bed dense bed
Figure 3.1: NOXSO desulfurizalion process applied in JFB syslem
The driving force for this flow of particles is the pressure difference between the dense and the lean bed. This pres su re difference is accomplished by fluidizing both beds with
different superficial velocities and, hen ce, two different porosities.
The dense beds are usually kept as small as possible and serve no other goal than the
transportation of solids (transport beds) and with this the solids flow control. Three dense
3 Process structure and process flowsheet
clean tlue gas to sbck NOx to power plant sulphur compounds to sulphur plant warm air
T
T
T
T
Adsorber Transport bed heater (Iean) heater (dense) regenerator (Iean) transport! cooler (Iean) coc Ier (dense)
f.\t
f.\;
f.\;
strippingf.\;
raw flue gas air air air methane/steam steam air air
Figure 3.2: NOXSO desulfurization process applied in JFB system
Figure 3.3 shows the solids pathway as a top view and as a three dimensional view ofthe IFB system.
3.2 Adsorber
lean bed: the adsorber
S02 and NOx are removed from the flue gas with efficiencies of respectively 95% and 90%. Clean flue gas is transported to the stack. The amount of sorbent needed to achieve this efficiency can be calculated as follows:
( '" 'f'mol.f1uegasYS02,in -'" 'f'mol.f1uegasYS02.0ut )M S
=F~-F~
s 100 s 100 With:YS02.in
YS02.out
Ms
F.
: Sulfur load after adsorption
: Sulfur load after regeneration : Molar flow flue gas
: Mole fraction S02 in raw flue gas
: Mole fraction S02 in clean flue gas
: Molar mass sulfur
: Mass flow sorbent (kg/s) The resulting sorbent flowrate equals 43.5 kg/s.
l.5 wt% 0.3 wt% 7.13 kmolels 2400.10-6 120.10-6 32 kg/kmole (3.1)
Ma and Haslbeck [Ref. 4] have presented an adsorber model equation based on the fluid bed model of gas phase plug-flow and solid phase mixed-flow assumptions:
1
Adsorber
8
Coolers
... .4 Lean bed Dense bedFigure 3.3 Schematic drawing ofJFB system
3 Process structure and process (lowsheet
..
.
",'" ,'
..
.
.. .. .. . " ... ', 4 .. ~ . . . ''':'4 ' , ' : .. ' .. ', ' . .d,' ::2
'
.
.
.
•
...
•
...
.
...
"
: .
. ~ ",·
::,' >3':,'4
.
.
'"
'.' '.
,.
.
.
' .. ... . .... . '4 '-4· • 4 . . ''
.
..
:
... " ... :.~ . . ". .".
. ~-:. ','.' . . 4.
'
.1
"
.Heater
•
Regenerator
Over weir Through orifice3 Process structure and process {lowsheet (3.2) in which (3.3) (3.4) (3.5)
With the known sorbent flowrate, different combinations of height and area can be chosen
to accomplish the removal efficiency. Each combination results in a different pressure drop
and superficial velo city, as shown in figures 3.4 and 3.5.
9 ~ 8
'g
7 Ol 6 >""""'5 _ rJ) .~E
4 u'-' 'E 3 ~ 2 :s 1 Cf) 0 5Superficial velocity versus bed diameter
:::::~:::::::::::j:::::j:::::;:::::~:::::~::::~:::::j:::::;:::::;::ute:m\ina~:(dpi:=:=::$Q:qm):::
_ _ _ _ . . . 0_ 0" _ _ _ _ ~ _ _ _ _ _ ~ _ _ _ _ .~ _ _ _ _ .o. ____ .'. ___ _ ..I • • ___ • _____ ~ _____ L _ _ _ _ .... ____ ~ _ _ _ _ _ .Jo _ _ _ _ • _ _ _ _ _ L. _ . _.l.. ___ 0'
I I • , , , I , , • , , , I , , • , ____ .1. _ _ _ _ _ _ __ J _____ J _____ ~ _____ ... ____ . ' . ____ J • • ___ J _ • ___ 1 _____ I. ____ .1,. ___ • • ' . _ _ _ _ J _____ , _____ 1 _ _ _.'-__ • _ .' , I • , , , I I , , , , , I , , , , - ----:--_. - -:- - --~ --- - - t - --- -} ---- -l--- - - -:- - - -- -:- - -- -.; - _ •• -t· - ---:. - - ---:-- ----:- - -- -~ -- ---t -- - - -~ - - --:- - . ---: ---- A:. ---- A:' ---. -. -- --t -- - -. ~. -•• -r -_. --:-----.:- ----~. ----;. ---:. ---:-. _ .. -;- -'. --; ---t --- - -!- - _. -; •••••. : . . .
.
; . . . -- -:- - - -;- -.
.
- ! - -, - --r. .
---;---:- --, ---;--, ---i - -- - -.
r , ---;. -, ----:-, ---:- --, --~-, ----i -, -- --l- - - - -:- -, , -- --; , ---,---.---"1---,- --r---r---,---.---·-,---'·----r---,---,--·, , " " " " " . , --,··---'---r- ---r·----, ---r----·'---,- ---.
, -' __ , A_of.
---r---'--- .. ---· , , , .,.----,.-.--, -·--·r-····'·· , , , , , .- . .,.--.-,---.
, :::: :~:-.
.. ...,. ~~ •• •• ~ ~. ;~ •. ~ .. ~. ;~ .• ••• ~ ~~ .~ ... ~ .""! •• ~ •• ,-. -.~. ~~ .. ~ ... ~; . -.. ~ .. ,....~.-.. -.. ~~ . -.. -.. ~~ .~ .. ...,. ~~ ... - .. ~;.~ .. -.. ~; . -•• -.. ~~ ."--... :::::::: , . . " . c·_--""' ... = ... -.. ;. -. -.; -. -.-: -_ • • • ~. --_ . . . -_ . _ . . --_ . _ . ---~. _ . _ . . . -_ . _ . . . . --_ . . . . --_ • • • -_ • • • ---~ • ---___ --- 0 -_ _ _ _ . . _ _ _ _ _ • _ _ • . . _ _ _ _ _ _ _ _ _ _ _ • I • , • • • , • , , • , • I I • , • --_ . _ . . . --_ " , . _ . -_ .. --_ . -• ----_ .. ----_ .. ----_ ' " ---_ . . _ ---_ . ----_ . ---~ ----___ ----+1- _ _ _ _ .. _ _ _ _ _ • __ _ _ _ .. _ _ _ _ _ ... _ _ _ _ • I I I • • , • • • . " I I , • • ----_ I .. _--_ .. I _----"'---_ I..
• _-_._ .. I _---_ •...
_--_ ... , _-_ ... _-_._ , .. , --_..
• ---I...
---_ ... • , _---_ .. I _---_._---_ • • .. _---_ ... • _--_. , 7 9 11 13 Bed diameter [m]Figure 3.4: Design ofthe adsorber: superficia/ ve/ocity versus bed diameter
Water is used to keep the adsorber at constant temperature. This supply equals 5.5 kg/s.
Sorbent make-up is added in the adsorber. The make-up rate depends on the (unknown)
3 Process structure and process flowsheet ~ 0.15 a::J
B
0.125g-
0.1...
'"C 0.075 Q) :; 0.05Pressure drop versus Bed Diameter
. ~ ----_. ----_ ... _. --.... _.
-
----
---, ... ---... , ---... , ----
-
--
_. ,.
, , , , , , , I --- ---_ ... , , _---, .... , ---.----.---... , , ---.. ---.---, , , , , ______________ " _ _ _ _ _ _ '- ______________________ , _______ • • ______________ , _____________ _________ J __________ _ , , , I , , , , , , , , ,::::::::::::::::::::::~::::::---:::::::::::::::::----:::::::::::::::r::::::::::::::::::::r::::::::
:
~ 0.025 ... ~ .. --.. -- .. -- ... --~---~---.--- ---~---Q) : : : : , , , , ~ O+---+'---~'---'r---r'----5 7 9 11 13 Bed diamete r [m]Figure 3.5: Design ofthe adsorber: pressure drop versus bed diameter
Taking 81 m2 for the bed surface, a superficial velocity of2.9
mis
is achieved, Togetherwith the bed height of 2.5 m, the resulting pressure drop is 5.5 kPa.
Dense bed: transport bed
This bed serves no other goal than to transport the sorbent particles to the first heater. It is fluidized by air and designed to have a minimum area.
3.3 Heater
lean bed: sorbent heater en NOx regenerator
Air coming from the cooler is heated to 842
oe
in a furnace and then used to heat sorbent particles from 113oe
to 683oe.
During the sorbent heating step all NOx is released from the sorbent particles_ The air leaving the heater containing the NOx is returned to the coal burner(s) ofthe electric power plant furnace.
As stated by Botterill [Ref. 1] and Howard [Ref. 2] heat transfer between gas and particles in a fluidized bed is very fast. Gas and particles reach their end temperature directly upon entering the reactor. This implies no limitation in heat transfer. The area and height ofthe lean bed are thus not determined by heat transfer limitations, but based on hydrodynamics only.
The amount of air flowing into the heater is deterrnined by the cooler. Therefore, the only design parameter is the inlet temperature of the air. This can be calculated with a simple enthalpy balance:
3 Process structure and process flowsheet
With:
~air : Air flowrate C p,air : Specific heat air
At the calculated air flowrate (see Cooler), the temperature ofthe inlet air then equals 842 °C.
The terminal velocity of the particles is the design parameter of the reactor. At the temperature ofthe heater (683°C), the terminal velocity ofthe smaUest particles equals
4.3
mis.
At the air flowrate of 136 kg/s (see Cooler), the area ofthe heater is chosen 121m2. The superficial velocity is then 3.1
mis
.
The height ofthe reactor is taken the same as the adsorber (2.5 m).Dense bed: transport bed
Like the transport bed from the adsorber this bed just transports the sorbent particles to the next bed (regenerator). It is fluidized by (a slip stream ofthe) hot air from_the air
furnace with a minimum area. ~
3.4 Regenerator
lean bed: suljilr regeneration
Removing ofthe sulfur compounds from the sorbent particles is accomplished by
fluidizing the lean bed with methane and steam. Reaction products (S02' ~S, CO2, COS,
CS2 and ~O) together with methane are fed to a sulfur plant. This could be a Claus unit, for which the ~S/S02 ratio is not on spec (should be 2: 1 instead ofthe calculated 1 :2). So, part ofthe S02 must be reduced to ~S in order to get the correct ratio.
Steam is used as transport gas as weU as stripping gas. Due to insufficient data on how to operate the regenerator, a highly empirical model is used to design the regenerator.
Existing data from a working pilot plant regenerator is extrapolated to a 150 MWe power plant. Because the NOXSO pilot plant regenerator is a moving bed reactor, gas flow rates are too low to use for a fluidized bed reactor. To increase flowrates, a recycle is used (see figure 3.6).
The recycle ratio (recycle st re am / stream leaving the reactor) is designed in such a way that residence time is the same as the moving bed regenerator (in the NOXSO proces) with reasonabie reactor dimensions. The natural gas inlet flow rate is chosen in such a way that the ratio of steam and natural gas at the inlet of the reactor equals the pilot plant data.
Recycle ratio
Natural gas flow rate Outlet S02 flow rate Outlet H2S flow rate
: 0.74 : 3.9 kg/s : 11.5.10-3 kmol/s : 4.8.10-3 kmol/s Lean Bed Sorbent Steam Methane Recycle
Figure 3.6: Sorbent regenerator
3.5 Cooler
lean and dense bed: sorbent cooler
3 Process structure and process {lowsheet
H2S, S02 to sulfur plant
Compressor
Sorbent particles leaving the regenerator are cooled in both the lean and the dense bed to a
temperature of 133
oe
with ambient air. Warm air leaving the cooler is further heated in afurnace and used as an input for the sorbent heater.
The design of the cooler is similar to that of the heater. The amount of air needed can be calculated with an enthalpy balance.
F.
C
p.sorbent T.,in+
rjJ air.leanC
p.air T;,ir,in=
F.
C
p.sorbent T.,1ean+
rjJ air.leanC
p.air T;,ir.lean (3.7)3 Process structure and process aowsheet
~ Cp,sorbent T.,lean
+
rfJair,dense Cp,air ~ir,in=
~ Cp,sorbent T.,out+
rfJair,dense Cp,air ~ir,dense(3.8)
81 121 12 121 41 41 120 113 680 683 575 568 222 133 2.9 031" 3.1 0.16" 0.68 0.27" 3.1 1.25 3.93 3.93 4.27 4.27 6.24 6.24 4.1 3.9 0.31 0.31 0.16 0.16 0.25 0.27 0.27 0.31 45.5 22.7 71.2 16.4 1.32 6.36 2.46 3.59 0.76 0.45 0.77 0.45 0.56 0.45 0.76 0.65 0.85 0.97 0.32 0.94 0.55 7.2 17.5 7.5 17.5 14.0 17.5 7.7 11.2 0.86 8.2 0.81 16 3.7 9.3 0.81 2.0 21 8.7 27 6.3 51 2.4 9.4 14 10.1 10.1 12 12 13.1 9.3 8 8 8 1.6 10.1 1 9.3 0.5 5.1 5.1
*: IncIuding the distributor plate ": Slip velo city
-3
Make Up Air
T
H2S, S02 to CLAUS
11.8410_/molls S024.82 10
km",
H2SfU J-JI-'III I~VA
I
Coal Burner
I
I
I
furnace
I"/ '\.
/ I"
"
V
"
/S
Adsorber
Heater
Regenerator
Cooler
xbent
113oG,
683 oC"
568 oC "-
133
~C"
H = 2.5 m
H = 2.5 m
H = 2.5 m
H = 2.5 m
/ / / / /
A = 81 m
2A = 121 m
2A = 121 m
2A=41 m
2(tor both lean
and dense beds)
/ I"' / I"' / I"' /
"
Flue gas
172 Nm
3 Is2400 ppm S02
781 ppm NOx
250C
Natural Gas, 3.9 kgls
Ambient Air, 136 kgls
- - -
AIR
I
F1 / I I ' ' \ .0J-R1 ~ STACK ~f---<~ . . r---,
,
,,
,
,
e
,
,
~---:~:
I
rmi(1OO)~--"""---_':"::~~
--ee
1--1
-~
-,,
R21 ! R3 1 R41 R5 1 R61 R7 RB 1 0,
, F20)
~
~---l---:il
FLUE GASt
Air Natural Gas Steam Air C5 Natural Gas 26 Rl ADSORBER,
,
",
,
~---B
" B
' '- -,
~ - - - FC)
~ ~-G
y
R5 REGENERATOR Cl - C6 COMPRESSORS -C6 l _ _ _ _ _ _ _ J4
Calculation of the equipment
All calculations have been do ne using the computer programs "MathCad 5.0+" and "Excel
4.0".
Interconnected Fluidized Bed
The minimum fluidization velocity can be calculated according to the Wen & Yu equation
[11]:
Umf
=(_77_J[~(33.72
+0.0408Ar)-33.7]
Pf dp
(4.1)
. hi hAr ( pfd/(pp -Pf)gJ' h II dA h' d b
In W C
=
77
2 IS t e so-ca e rc zme es num er.Usually, the bed porosity at minimum fluidization conditions - cmf - lies between OAO and
0.50. Here, 0.45 has been chosen.
The bubble size follows from the equation for aporous plate distributor according to Rowe [12]:
d ~ d
=
)U - U . h 0.75 . g-0.25eq b 0 mf (4.2)
in which Uo is the superficial gas velocity, equal to
tP
g.
A
The average bubble size - deq - is calculated with this equation at h=OAH (40% ofbed
height).
The bubbles rise at an average velo city of Ub
=
O.711~(gdeJ
according to Davidson andHarrison [12].
To ensure no (or little) entrainment occurs the superflcial gas velo city should be lower
than the free fall velo city of a particle. To find the tenninal velo city of free-falling particles
one can use the following equations, presented by Haider and Levenspiel and Kunii and Levenspiel [11]: and [ ] -1/3 2
U
=
U·
Pf
t t~Pp
- Pf)g (4.3,4)4 Calculation ofthe equipment
with (4.5)
Of course, the superficial velocity should be based on the smallest free fall velocity and therefore on the smallest particles.
The number of particles in a fluidized bed
(Np)
is calculated with N=
volume of particles in bed=
(1- Gb)( 1- Gmf )HAP volume of one particle 7r d 3
6
pin which Gb = Uo
~
Umf and UA = Uo - Umf+
U b with Ub = U b at deq =d
eq. A(4.6)
The total mass ofparticles in the bed is equal to the volume ofthe particles times the solids density, or in formula:
(4.7) Pressure drop
The pressure drop over the bed is calculated with:
(4
.
8)
The pressure drop over the distributer plate is taken 0.3 times the pressure drop over the bed.
Transport disengagement height: Height above which the elutriation rate faIls either not at all or slightly. Using reference 8, the resulting height equals about 10 m.
Orifice: Particles flow from the dense to the lean bed through an orifice. Using reference 9, the solids flux, area, pressure drop and gas leak are calculated and given in the next table.
Table 4.1 Orijice properties
From ... to Solids flux Aorifice LU> orifice Gas leak
[kg/m2/s] [m2] [Pa] [kg/sJ
Adsorber transport bed (Rl) to heater (R3) 354 0.12 6.4 0.23 Heater transport bed (R4) to regenerator (R5) 210 0.21 2.3 0 Regenerator transport bed (R6) to cooler (R7) 354 0.12 6.4 0.062 Cooler (R8) to adsorber (Rl) 166 0.26 2.2 0.17
4 Calculation ofthe equipment
Cyclones
Cyclones are ca1culated using reference 10. Cyclone MI is designed as a "high
throughput" cyclone. Cyclone M2 is designed as a "high efficiency" cyclone, due to the fact that M2 is followed by a compressor.
MI
At given throughput and chosen velo city of25
mis,
the resulting inlet duet diameter Dc can be ca1culated with:Area
=
0.28125 D; (4.9)M2
At given throughput and chosen velo city of 15
mis,
the resulting inlet duct diameter Dc can be ca1culated with:Area
=
0.1 D; (4.10)The dso ofthe particles leaving the cyclones can be calculated using the sealing factor:
(4.11)
For MI, the d2 equals 14 )...lm. For M2, d2 equals 7 )...lm.
The grade efficiency is deterrnined using the standard grade efficiency curve in reference 10.
Pressure drop in the cyclones is calculated with:
(4.12)
Resulting pressure drop is 0.1 bar for MI and 0.001 for M2.
Furnace heater
The amount ofnatural gas needed to heat 136.1 kg/s of air from 192°C to 790°C can be calculated with:
Hair,in - Hair,out 1
=
Mlcombustion TJ
4 Calculation ofthe equipment
The efficiency ofthe fumace is made up oftwo parts: bumer efficiency and heat transfer efficiency. Both are taken 90%, so the overall efficiecy equals 81 %.
Compressors
Compressors are designed using ChemCad lIl. At given flowrates and pressure ratios, the duty of the compressor is calculated. Reference 10 is used to determine the type of compressor at given flowrate.
5
Mass and energy balances
In the following tables, the component stream properties are given. "Net Flue Gas" refers
to flue gas without S02 and NOx'
STREAM COMPONENTS
Net Flue Gas S02 NOx H20 N2 CH4 H2S C02 Air TOTAL: STREAM COMPONENTS Net Flue S02 NO x H20 N2 CH4 H2 S CO? Air TOTAL: M IN KG/S Q IN kW Gas 1 M 205.4 1. 09 0.21
-206.7 1 Q -91432 2 3 4 5 M M M M 205.5 205.3 205.3 -1. 09 0.055 0.055 -0.21 0.021 0.021--
5.46 5.46 ---
-
---
---
-
---
-
---
4.43 4.43 4.66 206.7 215.3 215.3 4.66 2 3 4 5 Q Q Q Q-
-
-
-- --
--
-
-
--
-
-
---
---
-
---
- ---
-
---
-
-
1398 96289 98612 98612 1398STREAM COMPONENTS Net Flue Gas
S02 NOx H20 N2 CH4 H2S C02 Air TOTAL: STREAM COMPONENTS Net Flue Gas
S02 NOx H20 N2 CH4 H2S CO? Air TOTAL: M IN KG/S Q IN kW 6 M
-4.66 4.66 6 Q -1398 13985 Mass and energv balances
7 8 9 10 M M M M
-
-
-
--
-
-
--
-
0.19 ---
---
-
-
--
-
-
--
--
--
-
-
-135.46 0.67 136.36 -135.46 0.67 136.55 -7 8 9 10 Q Q Q Q --
- ---
-
--
---
-
-
--
- ---
-
-
---
---
-
- -176602 883 147118 -176602 883 147118-STREAM COMPONENTS
Net Flue Gas
S02 NOx H20 N2 CH4 H2S CO? Air TOTAL: STREAM COMPONENTS
Net Flue Gas
S02 NOx H20 N2 CH4 H2S CO? Air TOTAL: M IN KG/S Q IN kW 11 12 M M
-
--
2.82-
-- 1. 97 1.18 4.52 2.69 9.86-
0.63-
1. 30 --3.87 21.1 11 12 Q Q
-
----
--
----
--
----
-3268 452735 Mass and energv balances
13 14 15 M M M
-
-
-2.82 0.74 2.08-
-
-1. 97 0.51 1. 45 4.52 1.18 3.34 9.86 2.57 7.29 0.63 0.16 0.47 1. 30 0.34 0.96-
-
-21.1 5.5 15.6 13 14 15 Q Q Q-
-
---
-- -
--
-
--
-
--
-
--
-
--
-
--
- -46360 12080 34280STREAM
COMPONENTS Net Flue Gas
S02 NO. H20 N2 CH4 H2S C02 Air TOTAL: STREAM COMPONENTS Net Flue Gas
S02 NO. H20 N2 CH4 H2S CO? Air TOTAL: M IN KG/S Q IN kW 16 17 M M
-
-2.08--
-1. 45 0.38 4.52 -10.0 -0.47 -0.96--
-19.5 0.38 16 17 Q Q ---
--
----
--
----
--
-37548 287-5 Mass and energv balances
18 19 20 M M M
-
-
--
-
--
-
-0.38-
---
--
-
--
-
--
-
--
136.2 136.2 0.38 136.2 136.2 18 19 20 Q Q Q-
-
--
- ---
--
-
---
-- ---
-
--
- -- --300 40885 42393
5 Mass and energl!. balances
STREAM 21 22 23 24 25
COMPONENTS M M M M M
Net Flue Gas
-
-
-S02 -
-
--
-
---
--
-
--
---
--co
--
-Air 90.7 45. 4 136.1 136.1 136.1 TOTAL: 90.7 45. 5 136.1 136.1 136.1 STREAM 21 22 23 24 25 COMPONENTS Q Q Q Q QNet Flue Gas - -
-S02
-
- -NOx - - -H20-
-
-N2-
-
-CH4 - - -H2S-
-
-CO - --Air - - -TOTAL: 28227 141 66 65036 166459 177485 M IN KG/S Q IN kW
STREAM COMPONENTS
Net Flue Gas
S02 NOx H20 N2 CH4 H2S C02 Air TOTAL: STREAM COMPONENTS
Net Flue Gas
S02 NOx H20 N2 CH4 H2S CO? Air TOTAL: M IN KG/S Q IN kW 26 M
-0.70 1. 59 -2.29 26 Q-5 Mass and energv balances
27 28 M M -'
-2.82--
-1. 97 5.46 4.52 -9.86 -0.63 -1. 30--
-21.1 5.46 27 28 Q Q-
--
--
--
573-
--
-, ---
---45273 573
FVO No.3123
5 Mass and energv balances
In the following figure, the mass and heat balance is presented in a schematical way. Gas leaks through the orifices are also taken into account.
MASS-
ANDIN FOR-
HEAT-
RETURN OUTWARD
BALANCE.
M M . M Q fR6MRB
M Q Q&\..
Q ~200'13
b
3
I Lf 32- I "Cl
/ .-: 1..20b,7
3b
ltS
S
?
w
r-- --!
--~~~
I'J
b28
3
5 Yb
51
3
2~ 7'"
Rl
~ 1 ' -Lr3/
b.9
..-- -- --
-
,21f~'lv
-0,
(~
/3
q []
5C2
b4,bb
:;-), S-
vJ f- - i - -...
, ,-
JLI
4
5
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R2
'-436'
, j
---1
3 '2, ('S/Lf
-l...o c:)BLf
.
1
8bl
'L
. I 4 .'2/~3
9
fJb
f'L
Mi
/ , ..-:,.
, GL
0/23
,11 -.--gO}3
t~-
- -/36, /
/l?Lff)Ç
' - - -.
/1026
2~ - --'/3'5
s- 1-W'
~
f-A
/~
b
602.
\(Z3
L ,-Lf3
I s-.--S-Joq/
0/68
8 "-.../-
-IN FOR-WARD M M Q Q
J~IS-~ :3,~ ~4t1 I~/3
3268
~32:?
°2.
fJi-I
3
16g?-) 5:
6
I'3lf2é3D
//3D;'2-
c,/
D
8Bc;-/:;-0
B
L{:;, );
/L('b-:;
-CONTINUED
t-Rbt'\~~ RETURN OUT*1
M M Q Q.~~
J
Q /~~ ~
R
Lf
,V
~
/3~/S:;
/Vi/l
B
0 - / 0- , 1 - - - -Lf3/~
'V
5f2l{Z
,-,b \
~5
M
--~ ~ 11~ /Î
,-1.12,2
q~C5
- 0- --Lfl{
/07-I /
k-0/38
w
f-\8-
-.. I ~
öO
~~I.IG
0
106
fZ6~
~I~
//4
1\ 100'-21
11
I
'2...1_'
V
-1-YÇ2]3
~
41.,,2
-Ml
t- ..,.L13::}o3
r -\!f'V2
I, /
W ~2.-- -1-1-I
'
j /~Ç213
~
'Z- \ ,I
I
elf
-- é1b3bO
,I
I II
~I
• 13 _!12080
1 1,\ç
-
ç
IT
/<;;" Iy I ... )..
r-':JJ
jo
II
I~ ,c6
'v
~
1~28
2'2.'1-T
~
1\
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I I --1
~
V
ZI,4
1.
3
9
3
-_,,21
~~
n :--
25
L/2/l
1/.
3
2.LJ 'L'l- - JIN FOR-
CONTINUE
D
WARD M M Q f~Cl\'\ Q 2..} 2'2.1
R7-'\ l
.
,
R8
r---J
I1 23 l~--/O/1j2s
2
,
.3
J,.~
Fl
-/-GL
1-,..--/ 3b,
I
- //bbLf::;q
'\ 2y \i .J,
-
-,
\ ' /1,01\1
,
I-
--
-'
I
- -SoU DSGL :::
cs
Asl fAk 'IH
Rou.Gft.oQ:Ct=('cE
RETURN OUT M M Q Q
/36/ /
65036
DJ?-71
L!
2..-
/2
"2
I/OS-6
Equipment list and specification forms
In
this chapter the most important equipment have been summarized.Rl R2 R3 R4
Adsorber Adsorber Heater Heater
Reactor bed ort bed
1.7/1.1 1.3/1.1 1.2/1.0 1.2/1.0 120 113 680 683 1010 202 1515 150 10.1 10.1 12 12 8 1.6 10.1 1 12.5 12.5 12.5 12.5 resistant resistant R5 R6 R7 R8
Regenerator Regenerator Cooler Cooler
Reactor rt bed 1.8/1.2 1.211.0 1.1/1. 0 1.111.0 575 568 222 133 1523 58 510 510 13.1 9.3 8 8 9.3 0.5 5.1 5.1 12.5 12.5 12.5 12.5 SOi~S SOi~S resistant resistant
*: per compressor
6 Equipment list and specification forms
206.7 0.8/0.9 1.0/1.2 2400 85 160/183 697 820 6 S02 resistant C5 0.6/0.6 1.0/1.2 3398 85 110/118 12 14 1 4.7 1.2/1.4 1.0/1.3 2352 85 25/50 101 119 1 C6 136.2 1.2/1.3 1.0/1.1 815 85 25/36 417 491 3 136.1 0.3/0.4 1.0/1.2 5825 85 790/842 763 898 9 e 21.1 0.3/0.3 1.0/1.2 6796 85 575/596 467 549 2 SO/.f~S resistant
6 Equipment list and specification forms
25
15
l.1
l.0
0.1
0.008
120
575
3.4
3
.
7
13.7
16.4
3 42.3
3
.
7
S
resistant7
Process control
Solidflow
The solid flow in the IFB system is controlled by making one transport bed lirniting in solid flow. Changing the conditions in this bed will change the flow in the entire IFB system. The transport bed of the adsorber is used as this "controlling bed" .
Pressures inside the IFB
The pressure inside IFB system will be controlled by four pressure controllers, each one measuring the pressure in the free board zone. Temperature controllers are used for the cooler(s) and heater to control the gas feed and feed temperature.
Coal bumer air supply
Ambient air to the coal burner (power plant furnace) is controlled by a flow controller, which measures the amount of air corning from the heater. By measuring the amount of natural gas in the regenerator recycle a flow controller controls the feed of fresh natural gas.
Adsorber
Water sprayed into the adsorber is used to control the temperature in the adsorber. Heater
The temperature in the heater is controled by the natural gas supply to the furnace.
Regenerator
The recycle ofthe regenerator is controlled by a flow controller. Because the ratio of natural gas and recycle stream must be kept constant, the natural gas used in the regenerator is controlled by the same flow controller (ratio controller).
Coolers
All the air leaving the coolers is used in the heater. For safety purposes, a vent is used in st re am 23 to control the pressure in the cooler. The temperature in the coolers is
controlled by the air supply to the coo\er. The same controller used for the overall air supply to both coolers is also used to control the amount ofthat air passed to the lean bed. This ensures that the ratio of air going to the lean and the dense bed is constant. .
8
Safety, health and environmental aspects
8.1 HAZOP study
In designing new process plants a lot of measures have to be taken to reduce the safety, health and environmental risks. A convenient way in achieving this could be a Hazard and Operability Study (HAZOP). As an example a (shortened) checklist has been coUected in table 8.1 (source: 'Checklist processing plants' ofthe Dutch Labour Inspectorate, 1986, Ref. 7). Goal ofthe HAZOP study: "to achieve an optimum standard of safety in the design, construction, operation and maintenance of new processing plants, likewise modifications in existing plants" (citation from Dutch checklist, Ref. 7).
In the design ofthe IFB module the selection and location are determined by the selection and location of the electric power plant itself. The personnel too is part of the working staff ofthe power plant. Points concerning the SHE aspects wiU be made clear in the next paragraphs.
8.2 Safety
Within this design the main part is formed by the IFB system. A permanent control of the fluidization conditions is necessary because a faU down in the gas stream wiU turn the fluidized bed into a packed bed, which may lead to the formation of hot spots. Especially in case of exothermic reactions - e.g. in the adsorber section - this would be disastrous.
The regenerator is another important section which needs a close foUow up. The methane stream can easily cause fire wh en it is in contact with oxygen (or air). So this contact has to be avoided. Therefore, the particles should flow from the heater to the regenerator with less or no gas leakage, because the heater is fluidized by air. A solution to this problem could be a J-valve as a particle flowing mechanism.
8 Safetv. health and environmental aspects
All sections of the IFB system can be approached directly from outside the system. This is a safe(r) and easy way for checking the system (sections).
8.3 Healtb
Concern of health mainly deals with the concern of health of the personnel at the plant. Serious problems occur ifthe personnel get into contact with S02, NOx or ~S. Personal monitoring should be applied if one has to work in the neighbourhood of the adsorber (S02 and NOJ, heater (N0J or the regenerator (S02 and ~S). MAC va}ues for S02,
~S and NOx (=NO
+
N02) have been listed in table 2.4.8.4 Environmental aspects
Of course, the ultimate goal of this PDA is to reduce the S02 and NOx ernission to the atmosphere in order to reduce the environmental effects ('acid rain'). However, one has to bear in rnind that there are spots in the plant where the concentrations of SOif~S and NOx are higher than in the flue gas stream. So, at an unexpected ernission of gas at a part ofthe plant the effects to the direct environment ofthe plant can be large.
9
Economical aspects
To estimate the (process) costs the methods described by Montfoort [Ref 5] have been
used (1$
=
Hfl1.70).9.1 Process costs
The total yearly costs wi11 be given by:
KT = 1. 13 Kp +2.6L+0.13!
in which: ~: production costs (variabie costs)
L : labour costs
I : investment costs
The total yearly costs were calculated at 85.5 M$.
The different terms will be calculated in the next paragraphs.
9.1.1 Variabie costs
(9.1)
These costs consist of the price to be paid for raw materials and utilities. In this process
these are: (low pressure) steam, natural gas, cooling water (process water) and electricity.
Table 9.1 specifies the costs.
Table 9.1: 0.15 $/Nm3 2.1.108 31.7 coo water 1.47 $/m3 157.2.103 0.23 electricity 0.08 $/kWh 1.26.108 kWh 10.1 TOTAL So ~ = 42.2 M$/yr.
Note that natural gas determines the biggest part of these costs.
9.1.2
.
Labour costs
9 Economical aspects
kN
P =
CO
.
76 (9.2)in which: p
=
productivity in man hour per ton flue gask = special distinction factor between discontinuous and continuous pracesses
N = number of units in the process
C = capacity in ton flue gas per day
The factor k had a value of l.7 for a continuous process in 1986. Assuming an efficiency
increase of 6% per year, k can be estimated at l. 7 (1 -0.06)9
=
0.97 for 1995.The capacity of flue gas is 172.28 Nm3
/s which is equal to 17.9 kton/day. Most difficult part of the relation is the number of units in the process. Here th ere has been chosen for 6
units, viz. 4 sections within the IFB system, one section for the heating of air and one
section for the combustion of coal (thus the boiler furnace). With this the productivity can
be calculated to be 3.4.10-3 man hour per ton.
The number ofpersonnel needed to operate the plant can thus be calculated:
N =pCN
p 24
(9.3)
which gives a number of personnel of 15.
Taking an average salary of $35,000 per year this means that the labour casts can be estimated at $525,000 per year.
Of course, the calculated number of personnel is a minimum one: there has to be supervision personnel too. Because the process in this PDA is a part of the electric power plant as a whole the contral can be done trom one control room and so the estimation of
the labour costs of contra I personnel can't easily be done.
9.1.3 Investment
costs
The investment casts can be subdivided into investments in:
IB: process units IA: auxiliary units
IL: non material (like know-how, start-up)
Iw: stocks, capital
IB determines 64 %, IA 16%, IL 14% and Iw 6% ofthe total investment casts.
The investment casts of the process units can be estimated using the Zevnik-Buchanan
9 Economical aspects
and
in which: IB
=
investment costs in k$ N=
number of process units Cf=
complexity factorFt
=
temperature factor F p=
pressure factor Fm=
material factor p=
capacity in ktonlyr m = degression exponent (= 0.6)Cl
=
Chemical Engineering Plant Cost Index(9.4)
(9.5)
Following the method described by Montfoort [Ref 5] one can calculate a complexity factor Cf of 5.9.
The capacity is 5954 kton flue gas/yr based on a plant operating time of 8000 hrs/yr. Together with Cl
=
360 (1993) and a number of 6 process units this resuJts in 234.5 M$ of investment costs for the process units.The costs for the compressors and blowers can be estimated by two methods described by James M. Douglas [Ref 6]:
Gas compressors (K.M Guthrie):
IC
=
(M& S)(517.5)(bhP)082
(2.l1+
FJ280
= Installed Cost in $
(9.6)
in which: IC
M&S = Marshall & Swift inflation index (!rom 'Chemical Engineering')
(1993: 970)
bhp = hp with hp
= actual compressor power in horse power
0.9
= correction factor for various types of compressors
Turbo blowers (M.S. Peters and K.D. Timmerhaus): PC
=
(M&S).39.7.Q0529
260 ~ in which: PCQ
=
Purchased Cost in $ = throughput in ft3/min (9.7)9 Economical aspects
When using turbo blowers for the gas feed to the cooler, heater, regenerator (recycle) and adsorber and using compressors for the other gas feeds the total compressor investment costs can be calculated at 6.9 M$.
With this the total investment costs are 234.5+6.9 = 280.7 M$. 0.86
9.2 Return On Investment
The return on investment (ROl) is the average return per year over the investments and is defined as the annual profit (after taxes) divided by the total investment without the non-material investment costs:
ROl
=
PR .100%1
PR = profit after taxes
I = 0.86·280.7 = 241.4 M$
(9.8)
The annual receipts from sales for this process consist of the 'profit' trom selling the high grade sulfur (ifthe off-gas treater is a Claus plant). The 150 MWe plant produces a sulfur stream of 16,449 ton/yr with a value of 40 $/ton. This profit can therefore be estimated at 0.66 M$. The process is just a new module within an existing plant. Therefore, one can't actually speak of the profit of this module. Furthermore, the total costs of this process are much higher than the income trom selling the sulfur. In order to show how the calculation ofthe ROl can be made the assumption has to be made that the electric power plant itself makes its profit out of selling the electricity and the sulfur. A 150 MW electric power plant pro duces 1.2.109 kWh of electricity per year (based on 8000 operating hours per
year). With a selling price of 0.08 $/kWh this results in a profit of96 M$. In table 9.2 the ROl is calculated.
Table 9.2: Calculation Return On Jnvestmenf
Annu 96.66 M$ Total costs 85.5 M$ 11.2 M$ 1.12 M$ 10.1 M$ 5.04 M$ 5.04 M$
9 Economical aspects
9.3 Internal Rate of Return
In this method the cash flows are recalculated to the present value over the project time using a return percentage, so that the sum ofthe recalculated cash flows over the project time is zero. Assuming a project time of 10 year the Intemal Rate of Return (IRR) can be calculated according to table 9.3 and formula 9.9.
Internal Rate of Re/urn: the cashflows per year
o
-241.41 - 9 6.16
10 45.5
The cash flow per year is equal to the net income plus the depreciation. For year '0' the cash flow consists ofthe total investment costs without the costs for non-material, so 86% ofthe total investment costs
=
241.4 M$. For the last year (10) the cash flow also includes the capital and the remaining value of the investment.The IRR can now be found solving the equation:
-241.4 +6.16·
t((
1 r)+ ( 45.5t
0i=1
1+1RR
1+1RR
(9.9)
And with this IRR= -10.6 %. The IRR becomes positive for a project time ofat least 34 years.
9.4 Cost evaluation
As can be seen in the foregoing paragraphs the costs of this process are much higher than the (oniy) profit ofselling the high grade sulfur. The ROl (per year) is very low and the IRR becomes positive oniy after more than 30 years. It is quite obvious that the cost aspect of this IFB module should be treated like the IFB module itself: as a part of the electric power plant as a whoie.
The NOXSO 150 MWe module has a net maintenance and operating cost of 4.5 M$, so the costs ofthe IFB module as designed here are (at least) 19 times higher.
10 Conclusions and recommendations
To summarize the results, 172.28 Nm3/s offlue gas (from a 150 Mwe power plant) is fed
to an adsorber, in which 90% ofthe NOx and 95% ofthe S02 is removed. The module
produces 16,449 ton sulfur per year.
By starting the research ofthis PDA it became clear that at this moment not enough information is available to achieve a satisfying result. Although fluidized bed theory could be used, in designing the adsorber and regenerator much empirical relations had to be
used. The regeneration reactions (and so the kinetics) haven't clearly been understood,
which makes it impossible to implement these in a Fluidized Bed Design. Therefore, our
fiTSt recommendation would be a further investigation to the kinetics of the regeneration reactions within a Fluidized Bed Reactor.
As has been calculated the costs for this plant are almost 20 times higher than the costs of
the (comparable) NOXSO module, deterrnined for more than 55% by the production
costs. The investment costs (especially those for the compressors) will be higher in
practice, because no pressure drop had been taken into account for all the valves.
As has been calculated, the IFB system can be an alternative for the NOXSO process with a great advantage of less attrition of the sorbent particles.
Compared to the NOXSO module all the IFB 'reactors' are at one stage, which is the
reason for the (relative) large size. Especially the heater and cooler are large because of
the fact that the incorning gas stream reaches its end temperature very soon.
On the other hand, in the proposed plant design the adsorber (low temperature) and
regenerator (high temperature) have been placed far away from each other, so no extreme
List of used symbols and abbreviations
A area [m2]
AlT Auto Ignition Temperature [0C]
Ar Archimedes number [-]
bhp brake horse power [hp]
C capacity of flue gas [tonlday]
Cf complexity factor Zevnik-Buchanan method [-] Cl Chemical Engineering Plant Cost Index [-]
Cp,air specific heat of air [J/kg/K]
Cp,sorbent specific heat of the sorbent [J/kg/K]
Ct total number ofN~O sites [kmole/kgsorbena dl,2 mean diameter of particle (eq. (4.11)) [m]
db bubble diameter [m]
DCI,2 diameter of cyclone [m]
deq equivalent bubble diameter [m]
dp particle diameter [!lm]
ELair Explosion Lirnits in air [% in air] Fc correction factor for various types of compressors [-]
Fg flue gas flow [kg/sJ
Fs sorbent flow [kg/sJ
g gravitational acceleration [rn/s2]
h height [m]
H(bed) height of the bed [m]
I total investment costs
[$]
IA investment costs for auxiliary units
[$]
IB investment costs for process units[$]
IL investment costs for non-material[$]
Iw investment costs for stocks, capital[$]
IC Installed Cost for compressors
[$]
IFB Interconnected Fluidized Bed
lRR Internal Rate of Return [%]
k distinction factor in eq. (9.2) [-] Kl ratio of reaction rate constants [Pa-I]
~ reaction rate constant [Pa-2s-l]
K2 ratio of reaction rate constants [Pa-I]
~
production costs[$]
KT total yearly costs
[$]
L labour costs
[$]
m degression coefficient [-]
~
adsorber sorbent inventory [kg]Ms molar mass sulfur [g/mole]
M&S Marshall and Swift inflation index [-] MAC Maximal Allowable Concentration [ppm]
List ofused svmbols and abbreviations
MIE Minimal 19nition Energy [J]
N number of units in the process
[-]
Np number of particles (chapter 4) [-]
Np number of personnel (chapter 9) [-]
P
productivity [man hour/ton]PC Purchased Cost [$]
PDA Preliminary Design Assignment
Q throughput [ftJ/min]
Ql,2 flow rate (eq.
(4
.
11»
[m3/h]re radius of exit pipe (eq.
(4.11»
[m]rt radius (eq.
(4.12»
[m]ROl Return On lnvestment
Sa sulfur load after adsorption [wt%]
Sr sulfur load after regeneration [wt%]
T air,dense outlet air temperature dense bed cooler
[OC]
T air,in inlet air temperature
[OC]
Tair,lean outlet air temperature lean bed cooler
[OC]
Tair,out outlet air temperature
[OC]
Ts,in inlet temperature solids flow
[OC]
Ts,lean inlet temperature solids flow lean bed cooler
[OC]
Ts,out outlet temperature solids flow
[OC]
TDH Transport Disengagement Height
Uo superficial gas velocity
[mis]
UI inlet duct velo city cyclone
[mis]
u2 exit duct velocity cyclone
[mis]
Ub bubble vel 0 city
[mis]
Umf superficial gas velocity at minimum fluidization
[mis]
Ut terminal velocity
[mis]
Xa
initial sorbent conversion factor [-]YNo xo inlet NOx mole fraction [-]
y S020 inlet S02 mole fraction [-]
YS02in mole fraction S02 in (raw) flue gas [-] YS°l"u1 mole fraction S02 in clean flue gas [-]
M cyclone pressure drop [mbar]
~P12 solid-fluid density difference (eq.
(4.11»
[kg/m3]Eb bubble fraction [-]
Emf voidage at minimum fluidization [-]
11 viscosity [Pa·s]
11 efficiency (chapter
4;
eq.(4
.
13»
[-]fll,2 fluid viscosity (eq.
(4
.
11»
[Pa·s]Pr gas density [kg/m3]
Pp particle density [kg/m3]
<l>air,dense <l>air,lean <l>g <l>mol,f1ue gas <l>NO x <l>S02
air flow rate dense bed cooler air flow rate lean bed cooler gas flöw rate
molar flow flue gas NOx removal fraction S02 removal fraction
List ofused svmbols and abbreviations
[kg/sJ
[kg/sJ
[m3/s] [mole/s][-]
[-]References
1. Howard, lR., Fluidized bed technology principles and applications, NY USA, 1989 2. BotterilI, lS.M., Fluid-bed heat transfer, Academie Press, London, 1975
3. Yeh, lT., W.T. Ma, HW. Pennline, lL. Haslbeck, J.I. Joubert, F.N. Gromicko,
Integrated testing of the NOXSO process: Simultaneous removal of SO 2 and NO x
jromflue gas, Chemical Engineering Communications, 114, pp. 65-88, 1992 4. Ma, W.T., J.L. Haslbeck, NOXSO SOjNOxflue gas treatment process
Prooi-of-Concept test, Environmental Progress, 12 no. 3, pp. 163, 1993
5. Montfoort, A.G., De chemischefabriek, Delft University of Technology , 1991
6. Douglas, lM., Conceptual design of chemical processes, McGraw-Hill Chemical Engineering Series, 1988
7. Checklist processing plants: Areas of attentionfor safe design (Checklist procesinstallaties: Aandachtspunten voor een veilig ontwerp), Dutch Labour Inspectorate, 1986
8. Geldart, D., Gasfluidization technology, John Wiley & Sons, 1986
9. Korbee, R., le. Schouten, e.M. van den Bleek, Modelling interconnectedfluidized bed systems, AIChE symposium series, 87.
10. Coulson, lM., J.F. Richardson, R.K. Sinnott, Chemical Engineering Volume 6, Pergamon Press, 1983
11. Kunii, D., O. Levenspiel, Fluidization engineering, Butterworth-Heinemann, second edition 1991
I
1 I Ir---,
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1 1 1 1 1 1 1 1STACK
•
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ee
/ / 1 \ "-0--
--- -
-
--Water
R1
R2
R3
II
FLUE GAS
t
0
Air
Natural Gas
Steam
1 1:: (01
1 1 L - .... - - - FC 1~----<0
_A~~---C-5---~~
Natural Gas
~---~26r---~--~R4
R5
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R7
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~-~----
-_-_-_-_-J _ - . J-~
-,
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- -_ _ -l I 1 1 1 1 1 1 _ _ _ _ _ .JF2
C3
R1 AOSORBER RS REGENERATOR C1 - C6 COMPRESSORS
REMOVAL OF S02 AND NOX FROM FLUE GAS FROM AN
R2 AOSORBER TRANSPORT BED
R3 HEATER
R6 REGENERATOR TRANSPORT BED
R7 COOLER
M1 - M2 CYCLONES
F1 CO AL BURNER
