Aspen Plus
Aspen Plus IGCC Model
Version Number: V7.0 July 2008 Copyright © 2008 by Aspen Technology, Inc. All rights reserved. Aspen Plus®, Aspen Properties ®, the aspen leaf logo and Plantelligence and Enterprise Optimization are trademarks or registered trademarks of Aspen Technology, Inc., Burlington, MA. All other brand and product names are trademarks or registered trademarks of their respective companies. This document is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. Aspen Technology, Inc. 200 Wheeler Road Burlington, MA 01803-5501 USA Phone: (1) (781) 221-6400 Toll Free: (1) (888) 996-7100 URL: http://www.aspentech.com
Contents 1 Introduction......................................................................................................... 1 2 Components ......................................................................................................... 2 3 Process Description.............................................................................................. 4 4 Physical Properties............................................................................................... 6 5 Chemical Reactions .............................................................................................. 7 Coal Gasification ............................................................................................ Desulfuration................................................................................................. Power Generation........................................................................................... WGS ............................................................................................................ Methanation ..................................................................................................
7 8 8 8 9
6 Simulation Approaches....................................................................................... 10 7 Simulation Results ............................................................................................. 13 8 Conclusions ........................................................................................................ 15
Contents
iii
1 Introduction
Global warming and global politics are driving the US and other countries towards the development of new energy technologies which avoid the use of petroleum and which allow for carbon capture and sequestration. This model simulates an Integrated Coal Gasification Combined-Cycle Power (IGCC) process with different sections of the plant modeled as hierarchy blocks (model templates). The model includes the following sections:
1 Introduction
•
Sizing of the coal
•
Gasification unit
•
Air Separation (ASU)
•
Gas cleaning unit
•
Water-gas shift unit
•
Ammonia unit
•
Methanizer
•
Combined cycle power generation
1
2 Components
The table below lists the components modeled in the simulation.
2
Component ID
Type
Component name
Formula
N2
CONV
NITROGEN
N2
O2
CONV
OXYGEN
O2
AR
CONV
ARGON
AR
COAL
NC
BIOMASS
NC
H2O
CONV
WATER
H2O
CO
CONV
CARBON-MONOXIDE
CO
CO2
CONV
CARBON-DIOXIDE
CO2
C
SOLID
CARBON-GRAPHITE
C
COALASH
NC
S
CONV
SULFUR
S
COS
CONV
CARBONYL-SULFIDE
COS
H3N
CONV
AMMONIA
H3N
H2S
CONV
HYDROGEN-SULFIDE
H2S
O2S
CONV
SULFUR-DIOXIDE
O2S
O3S
CONV
SULFUR-TRIOXIDE
O3S
H2
CONV
HYDROGEN
H2
CH4
CONV
METHANE
CH4
CL2
CONV
CHLORINE
CL2
HCL
CONV
HYDROGEN-CHLORIDE
HCL
S-S
SOLID
SULFUR
S
NH4+
CONV
NH4+
NH4+
H3O+
CONV
H3O+
H3O+
HCLO
CONV
HYPOCHLOROUS-ACID
HCLO
NH4CL(S)
SOLID
AMMONIUM-CHLORIDE
NH4CL
CLO-
CONV
CLO-
CLO-
CL-
CONV
CL-
CL-
OH-
CONV
OH-
OH-
NH4CL
CONV
AMMONIUM-CHLORIDE
NH4CL
2 Components
Component ID
Type
Component name
Formula
AMMON(S)
SOLID
AMMONIUM-HYDROGENSULFITE
NH4HSO3
NH4HS(S)
SOLID
AMMONIUM-HYDROGENSULFIDE
NH4HS
SALT1
SOLID
AMMONIUM-SULFITE-HYDRATE
(NH4)2SO3*W
SALT2
SOLID
AMMONIUM-SULFITE
(NH4)2SO3
HSO3-
CONV
HSO3-
HSO3-
HS-
CONV
HS-
HS-
SO3--
CONV
SO3--
SO3-2
S--
CONV
S--
S-2
S2
CONV
SULFUR-DIATOMIC-GAS
S2
S3
CONV
SULFUR-TRIATOMIC-GAS
S3
S4
CONV
SULFUR-4-ATOMIC-GAS
S4
S5
CONV
SULFUR-5-ATOMIC-GAS
S5
S6
CONV
SULFUR-6-ATOMIC-GAS
S6
S7
CONV
SULFUR-7-ATOMIC-GAS
S7
S8
CONV
SULFUR-8-ATOMIC-GAS
S8
MEOH
CONV
METHANOL
CH4O
Of the 45 components specified, COAL, BIOMASS and COALASH are nonconventional solid components. The only properties calculated for nonconventional components are enthalpy and density. Aspen Plus includes special models for estimating these properties for coal and coal-derived materials. See section 4 Physical Properties for more details.
2 Components
3
3 Process Description
Figure 1 shows the process flowsheet of the IGCC process.
Figure 1: IGCC Process Flowsheet
1
4
The coal feed is mixed with water in the Sizing section and undergoes crushing and screening. The PSD of BITUMOUS feed stream and the resulting coal slurry FUELOUT product stream in the Sizing section is shown in Table 1.
3 Process Description
Table 1 Interval
Lower limit
Upper limit
Weight fraction in BITUMOUS
Weight fraction in FUELOUT
1
0
20
0.11323618
0.19917354
2
20
40
0.04219685
0.09034502
3
40
60
0.05991239
0.1036473
4
60
80
0.09682933
0.1340567
5
80
100
0.1459255
0.17447921
6
100
120
0.1079199
0.12620008
7
120
140
0.0523056
0.06557651
8
140
160
0.04586571
0.0438711
9
160
180
0.0584937
0.02871873
10
180
200
0.27731484
0.03393179
2
The air separation unit (ASU) uses air to reach nearly pure Oxygen and Nitrogen. Using Radfrac-rigorous method to separate the air after pretreatment. The resulting Nitrogen product is 99.83 mole % pure, and the Oxygen product is 95 mole % pure.
3
The coal-water slurry is mixed with 95% O2 separated from air in the coal gasification section and converted into middle-low heating value syngas.
4
Corrosive components such as sulfide, nitride and dust are removed from the raw syngas in the cleaning section. The H2S-rich regeneration gas from the acid gas removal system is then fed into the Claus plant, producing elemental sulfur.
5
The Desulfuration section converts the hydrogen sulfide into sulfur.
6
To capture the carbon dioxide, a WGS reactor containing a two sections in series with intercooling converts a nominal 96% of the carbon monoxide to carbon dioxide.
7
The plant will operate at extremely low emissions of regulated air pollutants and will isolate carbon dioxide so that it can be captured. Ammonia is produced from Hydrogen and Nitrogen.
8
The carbon monoxide and Hydrogen are synthesized here into methane (by-product) in the Methanation section.
9
Following the cleaning section, the syngas is fed into the Combined Cycle Power Generation section, where the combustion energy is converted in electric energy at high efficiency.
3 Process Description
5
4 Physical Properties
The global property method used in this model is Peng-Rob. This method is used for the gasification and downstream unit operations. The SOLIDS property method is used for the coal crushing and screening section. The IDEAL property method is used in the CLAUS Hierarchy (Desulfuration section). The BWRS property method is used in the NH3 Hierarchy (the previous step of Methanation). The PR-BM property method is used in the Power Generation section. The enthalpy model for COAL, BIOMASS and COALASH is HCOALGEN and the density model for all components is DCOALIGT. The HCOALGEN model includes a number of empirical correlations for heat of combustion, heat of formation and heat capacity. You can select one of these correlations by specifying an option code in the Properties | Advanced | NC Props form The table below lists the specifications for this model: COAL Model Parameter
Heat of Combustion Standard Heat of Formation Enthalpy
Heat Capacity
Enthalpy Basis
BIOMASS
COALASH Code Value
Code Value
Correlation
Code Value
1
Boie correlation
1
1
1
Heat-ofcombustionbased correlation
1
1
1
Kirov correlation
1
1
Elements in their standard states at 298.15K and 1 atm
1
Correlation
The same as those for COAL
1
Correlation
The same as those for COAL
1
The density method DCOALIGT is specified on the Properties | Advanced | NC Props form. This model is based on equations from IGT (Institute of Gas Technology). The Aspen Properties User Guide, Chapter 6 gives more details on this.
6
4 Physical Properties
5 Chemical Reactions
The chemical reactions in this process are very complex. This model uses a relatively simple approach to represent the reactions. There are some reactions of by-products in this model. The reactors a re modeled with the built-in models RStoic, REquil and RGibbs. Reactions in each reactor and their specifications in the Aspen Plus model are listed as follows:
Coal Gasification Reactions in the COMB (RStoic) block Rxn No.
Specification type
Stoichiometry
Fraction
Base Component
1
Frac. Conversion
COAL→ H2O+O2+N2+C(Cisolid)+ COALASH+S-S(Cisolid)+CL2+H2
0.95
COAL
2
Frac. Conversion
BIOMASS →H2+O2+N2+C(Cisolid)+ COALASH+S-S(Cisolid)+CL2+H2
1
BIOMASS
Fraction
Base Component
0.9
COS
Reactions in COSHYDR (RStoic) block Rxn No.
Specification type
Stoichiometry
1
Frac. Conversion
COS + H2O
→
CO2 + H2S
Coal gasification is modeled using the Gibbs free energy minimization method in the RGibbs model named GASIFIER. The option “RGibbs considers all components as products in Products sheet” is selected so the model can determine the phase of each of the products as fluid or solid based on their properties. Note: The component yield of the coal decomposition product depends on the coal ULTANAL attributes, not on the yield specification. Calculator blocks BCONVRT and CCONVRT set up the appropriate coefficients to establish the yield.
5 Chemical Reactions
7
Desulfuration Reactions in BURNER (RStoic) block Rxn No.
Specification type
Stoichiometry
1
Frac. Conversion
H2S + 0.5 O2
2
Frac. Conversion
H2S + 1.5 O2
H2O + S
→
→
O2S + H2O
Fraction
Base Component
0.65
O2
1
O2
In this model, H2S are converted to S and SO 2, and finally S will become Sulfur.
Power Generation Reactions in the COMB-A (RStoic) block Rxn No.
Specification type
Stoichiometry
1
Frac. Conversion
CO + 0.5 O2
2
Frac. Conversion
H2 + 0.5 O2
→
→
Fraction
Base Component
CO2
1
CO
H2O
1
H2
Fraction
Base Component
1
CH4
Reactions in the BURNER (RStoic) block Rxn No.
Specification type
Stoichiometry
1
Frac. Conversion
CH4 + 2 O2
→
CO2 + 2 H2O
At very high temperature, it is assumed that components H2, CO and CH4 burn completely.
WGS Reactions in SHFT (REquil) and SHFT2 (REquil) blocks Rxn No.
Specification type
Stoichiometry
1
Temp. approach
CO + H2O
↔
CO2 + H2
The water gas shift (WGS) reactor converts most of the CO contained in the syngas into CO2 and H2
8
5 Chemical Reactions
Methanation Reactions in the METHANZR (REquil) block Rxn No.
Specification type
Stoichiometry
1
Temp. approach
CO + 3 H2
5 Chemical Reactions
↔
H2O + CH4
9
6 Simulation Approaches
Unit Operations – The major unit operations are represented by Aspen Plus models as shown in the following table (excludes reactor units):
Aspen Plus Unit Operation Models Used in the Model Unit Operation
Aspen Plus Model
Comments / Specifications
Coal Sizing
Crusher, Screen, Mixer
Reduce coal particle size
Air Separation
Flash2, Sep, Compr, HeatX, MHeatX, RadFrac, Heater
Separate Air into Oxygen and Nitrogen
Coal Gasification
RStoic, RGibbs, HeatX, Sep, Mixer, Flash2, Heater
Decompose coal to produce coal gas
Syngas Clean-up
RadFrac, Flash2, HeatX, Sep, Compr, Heater
Remove the corrosive components from the raw syngas
Desulfuration
RStoic, RGibbs, Flash2
Removal of the Sulfur
Power Generation
Compr, Mixer, Heater, Flash2, HeatX, Pump
Generate electrical power by utilizing the coal gas
Methanation
Mixer, REquil
Produce Methane
WGS
REquil, Flash2, HeatX, RadFrac
Convert the carbon monoxide to carbon dioxide, and then capture carbon dioxide.
NH3
RGibbs, HeatX, Sep, Mixer, Heater, Flash2
Produce ammonia
10
6 Simulation Approaches
Streams - Streams represent the material and energy flows in and out of the process. For the nonconventional solid components in the coal feed stream FEEDCOAL, the specification of PSD and component attributes is required. The values used are:
PSD Specification Interval
Lower limit
Upper limit
Weight fraction
1
0
20
0.11323618
2
20
40
0.04219685
3
40
60
0.05991239
4
60
80
0.09682933
5
80
100
0.1459255
6
100
120
0.1079199
7
120
140
0.0523056
8
140
160
0.04586571
9
160
180
0.0584937
10
180
200
0.27731484
Component Attributes PROXANAL
ULTANAL
SULFANAL
Element
Value
Element
Value
Element
Value
MOISTURE
9.535
ASH
9.66
PYRITIC
100
FC
50.9091914
CARBON
74.455
SULFATE
0
VM
39.4517217
HYDROGEN
4.955
ORGANIC
0
ASH
9.63908694
NITROGEN
1.585
CHLORINE
0.065
SULFUR
2.44
OXYGEN
6.84
Design-Specs, Calculator Blocks and Convergence - The simulation is augmented with a combination of flowsheeting capabilities such as Convergence, Design Specs and Calculator Blocks. The following tables outlines the key flowsheeting capabilities used in this model:
Design-Specs Used in the IGCC Model Spec Name
Spec (Target)
Manipulated Variables
ASU-DS-1
Sets the Heat-Duty of stream NETDUTY to 0 Watt
HX-2 hot temperature
GASFR-CSCBFW
Sets the temperature of stream CSCSYN1 to 700 F
CSC1BFW mass flow
GASFR- RSCBFW
Sets the temperature of stream B to 1400 F
RAD-BFW mass flow
6 Simulation Approaches
11
Calculators Used in the IGCC Model Hiearachy Name (Calculator name)
Purpose
SIZING
Sets the value of water stream to corresponding to solid stream
(PC-SLD1) ASU (COOLANT)
Sets the temperature of streams with the same value of TCW1
ASU
Specify the pressure of TURB-1, VALVE-1 and VALVE-3
(F-1) ASU (HUMIDITY) GASFR (BCONVRT) GASFR (CCONVRT) CLAUS (AIRFEED) WGS (STEAM)
12
Sets the water flow and temperature according to stream AIR-A. Modify the stoichiometric coefficient of each component in reaction 2. Modify the stoichiometric coefficient of each component in reaction 1. Sets the flow of stream BURNAIR to corresponding to flow of H2S Sets the flow of H2O in stream SYNGAS equal with the flow of CO in stream STEAM
6 Simulation Approaches
7 Simulation Results
The Aspen Plus simulation main flowsheet is shown in Figure 2.
Figure 2. IGCC Flowsheet in Aspen Plus
No errors occur in the simulation. Warnings occur due to physical property parameters PC and Freeze Point of carbon being outside the normal range. Key simulation results are shown in the following table:
7 Simulation Results
13
Key Stream Simulation Results Main Flowsheet Variable
Feed
Product
Value
Unit
Coal Feed
277431
lb/hr
Water for crushing
149386
lb/hr
O2 for Gasification
243840
lb/hr
Air for Separation
1053143
lb/hr
Air for Combustion
2993175
lb/hr
RAD-BFW
410000
lb/hr
Water for Water-gas-shift
30352
lb/hr
Water for Methanation
18015
lb/hr
Sulfur
1747
lb/hr
Methane
11827
lb/hr
Ammonia
3625
lb/hr
Power
447003
hp
Key Process Simulation results
14
Process Variable
Value
Coal Moisture before entering into Gasification furnace
44.8%
Coal Particle Size
80% of coal < 120
Gasification Furnace Temperature
1451
Combuster Temperature
1395
Air/fuelgas mole Ratio in combustor
6.84
Unit
mu
7 Simulation Results
8 Conclusions
The IGCC model provides a useful description of the process. The simulation takes advantage of Aspen Plus’s capabilities for modeling solid components. This includes tracking component attributes and particle size distribution, and estimating properties for coal. It also produces Methane, Sulfur and Ammonia as by-products. The model may be used as a guide for understanding the process and the economics, and also as a starting point for more sophisticated models for plant design and specifying process equipment.
8 Conclusions
15
