Environmental Engineering Reference
In-Depth Information
Table 1 Physical and chemical properties of Colombian coal
Proximate analysis (wt%)
Ultimate analysis (wt%)
Energy
Moisture
Volatile
matter
Fixed
carbon
Ash
C
H
N
S
O
LHV
(MJ/kg)
3.3
37.0
54.5
5.2
80.7
5.5
1.7
0.6
11.5
29.1
Fig. 1 Overall
fl
flow sheet of the CLC model in ASPEN Plus
The various process models used in ASPEN Plus
fl
flow sheet in Fig. 1 are
summarized in Table 2 . The coal devolatilization is de
ned by the RYIELD reactor,
followed by the gasi
cation of coal represented by the RGIBBS reactor. Another
RGIBBS reactor de
nes the actual syngas combustion and the corresponding
reduction of the oxygen carrier. These blocks together represent the fuel reactor.
The
flow sheet within the ASPEN Plus simulation package cannot model this entire
reaction with one reactor. As a result, the fuel reactor simulation is broken down
into several different reactor simulations. The air reactor is also modeled as an
RGIBBS reactor.
The energy balance of the CLC process model was analyzed using the input
values from the experiment of Sahir et al. ( 2012 ). The input values and the energy
requirements for the various units and streams in Fig. 1 are presented in Table 3 ;
this will be referred to as the baseline case in rest of the paper. Energy is consumed
mainly in the compressor processes. Compressed air is required in the air reactor to
regenerate Fe 2 O 3 from Fe 3 O 4 ; the air compressor for the combustor compresses the
air to 18 atm. Another compressor is used to compress the steam for the gasi
fl
er.
Table 2 Process models used in different parts of the CLC process in ASPEN Plus
Name
Model
Function
Reaction formula
DECOMP
RYIELD
Coal devolatilization
Coal
volatile matter + char
BURN
RGIBBS
Gasification
Char + volatile matter
CO 2 +H 2 O
FUEL-R
RSTOIC
Carrier reduction
reaction
3Fe 2 O 3 +CO 2Fe 3 O 4 +CO 2
3Fe 2 O 3 +H 2 2Fe 3 O 4 +H 2 O
AIR-R
RSTOIC
Carrier oxidation
reaction
4Fe 3 O 4 +O 2
6Fe 2 O 3
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