Aspen Plus

Aspen Plus IGCC Model

Version Number: V7.0 July 2008

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Contents iii

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

1 Introduction 1

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

2 2 Components

2 Components

The table below lists the components modeled in the simulation.

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 3

Component ID Type Component name Formula

AMMON(S) SOLID AMMONIUM-HYDROGEN-SULFITE NH4HSO3

NH4HS(S) SOLID AMMONIUM-HYDROGEN-SULFIDE 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.

4 3 Process Description

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.

3 Process Description 5

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.

6 4 Physical Properties

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 BIOMASS COALASH

Model Parameter Code Value

Correlation Code Value

Correlation Code Value

Correlation

Heat of Combustion

1 Boie correlation

1 1

Standard Heat of Formation

1

Heat-of-combustion-based correlation

1 1

Heat Capacity

1 Kirov correlation

1 1 Enthalpy

Enthalpy Basis 1

Elements in their standard states at 298.15K and 1 atm

1

The same as those for COAL

1

The same as those for COAL

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.

5 Chemical Reactions 7

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.

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

Reactions in COSHYDR (RStoic) block Rxn No.

Specification type Stoichiometry Fraction

Base Component

1 Frac. Conversion COS + H2O → CO2 + H2S 0.9 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.

8 5 Chemical Reactions

Desulfuration Reactions in BURNER (RStoic) block Rxn No.

Specification type Stoichiometry Fraction

Base Component

1 Frac. Conversion H2S + 0.5 O2 → H2O + S 0.65 O2

2 Frac. Conversion H2S + 1.5 O2 → O2S + H2O 1 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.

Specification type Stoichiometry Fraction

Base Component

1 Frac. Conversion CO + 0.5 O2 → CO2 1 CO

2 Frac. Conversion H2 + 0.5 O2 → H2O 1 H2

Reactions in the BURNER (RStoic) block Rxn No.

Specification type Stoichiometry Fraction

Base Component

1 Frac. Conversion CH4 + 2 O2 → CO2 + 2 H2O 1 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. 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

5 Chemical Reactions 9

Methanation Reactions in the METHANZR (REquil) block Rxn No. Specification type Stoichiometry

1 Temp. approach CO + 3 H2 ↔ H2O + CH4

10 6 Simulation Approaches

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

6 Simulation Approaches 11

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 NET-DUTY 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

12 6 Simulation Approaches

Calculators Used in the IGCC Model Hiearachy Name (Calculator name)

Purpose

SIZING

(PC-SLD1)

Sets the value of water stream to corresponding to solid stream

ASU

(COOLANT)

Sets the temperature of streams with the same value of TCW1

ASU

(F-1)

Specify the pressure of TURB-1, VALVE-1 and VALVE-3

ASU

(HUMIDITY)

Sets the water flow and temperature according to stream AIR-A.

GASFR

(BCONVRT)

Modify the stoichiometric coefficient of each component in reaction 2.

GASFR

(CCONVRT)

Modify the stoichiometric coefficient of each component in reaction 1.

CLAUS

(AIRFEED)

Sets the flow of stream BURNAIR to corresponding to flow of H2S

WGS

(STEAM)

Sets the flow of H2O in stream SYNGAS equal with the flow of CO in stream STEAM

7 Simulation Results 13

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:

14 7 Simulation Results

Key Stream Simulation Results Main Flowsheet Variable 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 Feed Water for Methanation 18015 lb/hr

Sulfur 1747 lb/hr

Methane 11827 lb/hr

Ammonia 3625 lb/hr

Product Power 447003 hp

Key Process Simulation results Process Variable Value Unit

Coal Moisture before entering into Gasification furnace 44.8%

Coal Particle Size 80% of coal < 120 mu

Gasification Furnace Temperature 1451 � Combuster Temperature 1395 � Air/fuelgas mole Ratio in combustor 6.84

8 Conclusions 15

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.