Aspen Plus IGCC Model.pdf

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					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 ............................................................................................ 7 Desulfuration................................................................................................. 8 Power Generation........................................................................................... 8 WGS ............................................................................................................ 8 Methanation .................................................................................................. 9 6 Simulation Approaches.......................................................................................10 7 Simulation Results .............................................................................................13 8 Conclusions ........................................................................................................15

Contents

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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: • • • • • • • • Sizing of the coal Gasification unit Air Separation (ASU) Gas cleaning unit Water-gas shift unit Ammonia unit Methanizer Combined cycle power generation

1 Introduction

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2 Components

The table below lists the components modeled in the simulation.
Component ID N2 O2 AR COAL BIOMASS H2O CO CO2 C COALASH S COS H3N H2S O2S O3S H2 CH4 CL2 HCL S-S NH4+ H3O+ HCLO NH4CL(S) CLOCLOHNH4CL Type CONV CONV CONV NC NC CONV CONV CONV SOLID NC CONV CONV CONV CONV CONV CONV CONV CONV CONV CONV SOLID CONV CONV CONV SOLID CONV CONV CONV CONV SULFUR CARBONYL-SULFIDE AMMONIA HYDROGEN-SULFIDE SULFUR-DIOXIDE SULFUR-TRIOXIDE HYDROGEN METHANE CHLORINE HYDROGEN-CHLORIDE SULFUR NH4+ H3O+ HYPOCHLOROUS-ACID AMMONIUM-CHLORIDE CLOCLOHAMMONIUM-CHLORIDE S COS H3N H2S O2S O3S H2 CH4 CL2 HCL S NH4+ H3O+ HCLO NH4CL CLOCLOHNH4CL WATER CARBON-MONOXIDE CARBON-DIOXIDE CARBON-GRAPHITE H2O CO CO2 C Component name NITROGEN OXYGEN ARGON Formula N2 O2 AR

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2 Components

Component ID AMMON(S) NH4HS(S) SALT1 SALT2 HSO3HSSO3-S-S2 S3 S4 S5 S6 S7 S8 MEOH

Type SOLID SOLID SOLID SOLID CONV CONV CONV CONV CONV CONV CONV CONV CONV CONV CONV CONV

Component name AMMONIUM-HYDROGENSULFITE AMMONIUM-HYDROGENSULFIDE AMMONIUM-SULFITE-HYDRATE AMMONIUM-SULFITE HSO3HSSO3-S-SULFUR-DIATOMIC-GAS SULFUR-TRIATOMIC-GAS SULFUR-4-ATOMIC-GAS SULFUR-5-ATOMIC-GAS SULFUR-6-ATOMIC-GAS SULFUR-7-ATOMIC-GAS SULFUR-8-ATOMIC-GAS METHANOL

Formula NH4HSO3 NH4HS (NH4)2SO3*W (NH4)2SO3 HSO3HSSO3-2 S-2 S2 S3 S4 S5 S6 S7 S8 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

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3 Process Description

Figure 1 shows the process flowsheet of the IGCC process.

Figure 1: IGCC Process Flowsheet

1

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.

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3 Process Description

Table 1
Interval 1 2 3 4 5 6 7 8 9 10 Lower limit 0 20 40 60 80 100 120 140 160 180 Upper limit 20 40 60 80 100 120 140 160 180 200 Weight fraction in BITUMOUS 0.11323618 0.04219685 0.05991239 0.09682933 0.1459255 0.1079199 0.0523056 0.04586571 0.0584937 0.27731484 Weight fraction in FUELOUT 0.19917354 0.09034502 0.1036473 0.1340567 0.17447921 0.12620008 0.06557651 0.0438711 0.02871873 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. 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. 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. The Desulfuration section converts the hydrogen sulfide into sulfur. 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. 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. The carbon monoxide and Hydrogen are synthesized here into methane (by-product) in the Methanation section. 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.

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5 6

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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 Code Value 1 Correlation Boie correlation Heat-ofcombustionbased correlation Kirov correlation Elements in their standard states at 298.15K and 1 atm BIOMASS Code Value 1 Correlation COALASH Code Value 1 Correlation

Heat of Combustion Standard Heat of Formation Enthalpy Heat Capacity

1

1 The same as those for COAL

1 The same as those for COAL

1

1

1

Enthalpy Basis

1

1

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.

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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 are 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. 1 Specification type Frac. Conversion Frac. Conversion Stoichiometry COAL→ H2O+O2+N2+C(Cisolid)+ COALASH+S-S(Cisolid)+CL2+H2 BIOMASS →H2+O2+N2+C(Cisolid)+ COALASH+S-S(Cisolid)+CL2+H2 Fraction 0.95 Base Component COAL

2

1

BIOMASS

Reactions in COSHYDR (RStoic) block
Rxn No. 1 Specification type Frac. Conversion Stoichiometry COS + H2O → CO2 + H2S Fraction 0.9 Base Component COS

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

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Desulfuration
Reactions in BURNER (RStoic) block
Rxn No. 1 2 Specification type Frac. Conversion Frac. Conversion Stoichiometry H2S + 0.5 O2 → H2O + S H2S + 1.5 O2 → O2S + H2O Fraction 0.65 1 Base Component O2 O2

In this model, H2S are converted to S and SO2, and finally S will become Sulfur.

Power Generation
Reactions in the COMB-A (RStoic) block
Rxn No. 1 2 Specification type Frac. Conversion Frac. Conversion Stoichiometry CO + 0.5 O2 → CO2 H2 + 0.5 O2 → H2O Fraction 1 1 Base Component CO H2

Reactions in the BURNER (RStoic) block
Rxn No. 1 Specification type Frac. Conversion Stoichiometry CH4 + 2 O2 → CO2 + 2 H2O Fraction 1 Base Component CH4

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. 1 Specification type Temp. approach Stoichiometry CO + H2O ↔ CO2 + H2

The water gas shift (WGS) reactor converts most of the CO contained in the syngas into CO2 and H2

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5 Chemical Reactions

Methanation
Reactions in the METHANZR (REquil) block
Rxn No. 1 Specification type Temp. approach Stoichiometry CO + 3 H2 ↔ H2O + CH4

5 Chemical Reactions

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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 Coal Sizing Air Separation Coal Gasification Syngas Clean-up Desulfuration Power Generation Methanation WGS NH3 Aspen Plus Model Crusher, Screen, Mixer Flash2, Sep, Compr, HeatX, MHeatX, RadFrac, Heater RStoic, RGibbs, HeatX, Sep, Mixer, Flash2, Heater RadFrac, Flash2, HeatX, Sep, Compr, Heater RStoic, RGibbs, Flash2 Compr, Mixer, Heater, Flash2, HeatX, Pump Mixer, REquil REquil, Flash2, HeatX, RadFrac RGibbs, HeatX, Sep, Mixer, Heater, Flash2 Comments / Specifications Reduce coal particle size Separate Air into Oxygen and Nitrogen Decompose coal to produce coal gas Remove the corrosive components from the raw syngas Removal of the Sulfur Generate electrical power by utilizing the coal gas Produce Methane Convert the carbon monoxide to carbon dioxide, and then capture carbon dioxide. Produce ammonia

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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 1 2 3 4 5 6 7 8 9 10 Lower limit 0 20 40 60 80 100 120 140 160 180 Upper limit 20 40 60 80 100 120 140 160 180 200 Weight fraction 0.11323618 0.04219685 0.05991239 0.09682933 0.1459255 0.1079199 0.0523056 0.04586571 0.0584937 0.27731484

Component Attributes
PROXANAL Element MOISTURE FC VM ASH Value 9.535 50.9091914 39.4517217 9.63908694 ULTANAL Element ASH CARBON HYDROGEN NITROGEN CHLORINE SULFUR OXYGEN Value 9.66 74.455 4.955 1.585 0.065 2.44 6.84 SULFANAL Element PYRITIC SULFATE ORGANIC Value 100 0 0

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 ASU-DS-1 GASFR-CSCBFW GASFR- RSCBFW Spec (Target) Sets the Heat-Duty of stream NETDUTY to 0 Watt Sets the temperature of stream CSCSYN1 to 700 F Sets the temperature of stream B to 1400 F Manipulated Variables HX-2 hot temperature CSC1BFW mass flow RAD-BFW mass flow

6 Simulation Approaches

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Calculators Used in the IGCC Model
Hiearachy Name (Calculator name) SIZING (PC-SLD1) ASU (COOLANT) ASU (F-1) ASU (HUMIDITY) GASFR (BCONVRT) GASFR (CCONVRT) CLAUS (AIRFEED) WGS (STEAM) 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 H2 S Sets the flow of H2O in stream SYNGAS equal with the flow of CO in stream STEAM Purpose Sets the value of water stream to corresponding to solid stream Sets the temperature of streams with the same value of TCW1 Specify the pressure of TURB-1, VALVE-1 and VALVE-3

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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

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Key Stream Simulation Results
Main Flowsheet Variable Coal Feed Water for crushing O2 for Gasification Air for Separation Air for Combustion RAD-BFW Water for Water-gas-shift Feed Water for Methanation Sulfur Methane Ammonia Product Power Value 277431 149386 243840 1053143 2993175 410000 30352 18015 1747 11827 3625 447003 Unit lb/hr lb/hr lb/hr lb/hr lb/hr lb/hr lb/hr lb/hr lb/hr lb/hr lb/hr hp

Key Process Simulation results
Process Variable Coal Moisture before entering into Gasification furnace Coal Particle Size Gasification Furnace Temperature Combuster Temperature Air/fuelgas mole Ratio in combustor Value 44.8% 80% of coal < 120 1451 1395 6.84 mu Unit

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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

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