11/7/2014

Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS

Modelling and Simulation of a Coal-fired Supercritical Power Plant Integrated to a CO2 Capture Plant

Elvis O. Agbonghae, Kevin J. Hughes, Derek B. Ingham, Lin Ma, Mohamed Pourkashanian

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Introduction (Process Flow Diagram of the Integrated Process)

Boiler

Steam Cycle

Flue Gas pre-treatment

CO2 Capture CO2

Compression

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Introduction (Key Features of the Power Plant)

Supercritical once through boiler with a SCR between the economiser and air-heater 2 ppmv NH3 slip in the SCR

Single reheat steam conditions: 241 bar/593 oC/593 oC (3500 psig/1100 oF/1100 oF) Cold reheat pressure: 45.2 bar

Steam Cycle Condenser pressure: 0.07 bar Saturation temperature is ~ 38 oC

Dedicated turbine (BFWPs) is used to drive the boiler feed water pumps Steam extracted from the IP-LP crossover is used to run BFWPs turbine BFWPs turbine isentropic efficiency is 80%

Steam Turbines Efficiencies HP turbine isentropic efficiency is 83.72% IP turbine isentropic efficiency is 88.76% LP turbine isentropic efficiency is 92.56%

Generator Efficiency is 98.5%

Aim and Objectives

4

1. To model and simulate an integrated process comprising a supercritical PC-power plant, a CO2 capture plant and a CO2 compression train within a single platform (Aspen Plus)

2. To quantifying the impacts of using different types of coal on the overall performance of the integrated process based on simulations. High volatile bituminous coal (Illinois No. 6) Sub-bituminous coal (Montana Rosebud) Lignite coal (North Dakota)

3. To quantify the impacts of important operating parameters of the CO2 capture plant on the overall performance of the integrated process. Lean MEA solution CO2 loading and liquid/gas mass ratio Lean MEA solution temperature (absorber inlet) Flue gas temperature (absorber inlet) CO2 capture level

An Overview of the Methodology

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The complete integrated process was modelled with Aspen Plus, V8.4, and dedicated hierarchy blocks were used for sub-processes. Coal-fired boiler, which includes a simple Model for SCR. Steam turbine cycle. a simple model for FGD . CO2 capture. CO2 Compression.

The CO2 capture plant was optimally designed based on rate-based calculations.

Electrolyte-NRTL model adopted for the liquid phase of the VLE. PC-SAFT equation of state adopted for the gas phase of the VLE. HETPs calculated based on mass transfer theory. The column diameter and height of the absorbers and stripper arrived at

systematically using innovative method.

CO2 compression modelled based on parameters in a 2010 US DOE report. PC-SAFT equation of state used for CO2 Compression Multi-stage Compression with inter-stage coolers and KODs (the sixth stage is a pump)

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Coal Feed and Combustion Air required (Combustion Calculations)

Coal Feed required

Combustion Air required

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Coal Properties

Proximate Analysis: As-Received (%) Illinois No. 6 Montana Rosebud North Dakota Moisture 11.12 25.77 36.08 Volatile Matter 34.99 30.34 26.52 Ash 9.70 8.19 9.86 Fixed Carbon 44.19 35.70 27.54 Total 100.00 100.00 100.00

Ultimate Analysis As-Received C 63.75 50.07 39.55 S 2.51 0.73 0.63 H2 4.50 3.38 2.74 H2O 11.12 25.77 36.08 N2 1.25 0.71 0.63 O2 6.88 11.14 10.51 Ash 9.70 8.19 9.86 Cl 0.29 0.01 0.00 TOTAL 100.00 100.00 100.00

Heating Value As-Received HHV (Btu/Ib) 11666.00 8564.00 6617.00 LHV (Btu/Ib) 11252.00 8252.00 6364.00 HHV (kJ/kg) 27113.00 19920.00 15391.00 LHV (kJ/kg) 26151.00 19195.00 14804.00

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Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS

Fig 2: Approaches for modelling reactive absorption processes (Kenig et al., 2001)

Process Modelling Approach

The most rigorous and the most complex. Aspen Plus Model!

Reference: Kenig, E. Y.; Schneider, R.; Gorak, A. Reactive absorption: Optimal process design via optimal modelling. Chem. Eng. Sci. 2001, 56, 343-350.

Aspen Plus Model (Key features)

Rate-based approach

Reaction kinetics

Reactions in Bulk liquid

Reactions in Liquid Film

No concentration gradient in bulk phases

Film discretization

Electrolyte present only in the liquid phase

Charge balance (electrolytes)

Equilibrium at V/L Interphase

Rigorous VLE Model (Electrolyte-NRTL)

Model Validation (Specific Reboiler duty vs L/G)

1 2 3 4 5

3

4

5

6

7

8

9

10

11

12 Exp (A.1)

Model (A.1)

Exp (A..2)

Model (A.2)

Exp (A.3)

Model (A.3)

Exp (A.4)

Model (A.4)

Sp

. R

eb D

uty

(M

J/k

g C

O2)

L/G (kg/kg)

Reference: Notz, R.; Mangalapally, H. P.; Hasse, H. Post combustion CO2 capture by reactive absorption: Pilot plant description and results of systematic studies with MEA. Int. J. Greenhouse Gas Control 2012, 6, 84-112.

Pilot plant data from Notz et al. (2012).

Experiment sets A.1, A.2 and A.3 correspond to gas-fired condition.

Experiment set A.4 corresponds to coal-fired condition.

Model Validation (Profile Results, Experiment set A.4)

0 2 4

40

45

50

55

60

65

70

0 2 4

100

105

110

115

120

Absorber

Te

mp

era

ture

(oC

)

Packing height (m)

Exp (L/G = 2.0 )

Model (L/G = 2.0)

Exp (L/G = 2.6)

Model (L/G = 2.6)

Exp (L/G = 2.8)

Model (L/G = 2.8)

Exp (L/G = 3.3)

Model (L/G = 3.3)

Exp (L/G = 3.6)

Model (L/G = 3.6)

Exp (L/G = 3.9

Model (L/G = 3.9)

Exp (L/G = 4.5)

Model (L/G = 4.5)

Te

mp

era

ture

(oC

)

Packing height (m)

Stripper

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Optimal Design of the CO2 Capture plant

𝐹𝐿𝑒𝑎𝑛 𝐴𝑚𝑖𝑛𝑒 =𝐹𝐹𝐺𝑥𝐶𝑂2

Ψ

𝛼𝑅𝑖𝑐ℎ − 𝛼𝐿𝑒𝑎𝑛

𝑀𝐴𝑚𝑖𝑛𝑒

𝑀𝐶𝑂2

1 +1 − 𝜔𝐴𝑚𝑖𝑛𝑒

𝜔𝐴𝑚𝑖𝑛𝑒+ 𝛼𝐿𝑒𝑎𝑛

The lean amine mass flow rate can be calculated as follows:

What combination of lean loading, rich loading, liquid flowrate, and stripper pressure will optimise the following?

• Absorber and Stripper diameters • Absorber and stripper heights • Reboiler Duty • Condenser Duty • Pumps Duty • Heat Exchanger Area

Interested in the design method? A Summary of the design method will be given in the second paper presentation. Details of the design method can be found in our recent journal paper.

Agbonghae, E. O.; Hughes, K. J.; Ingham, D. B.; Ma, L.; Pourkashanian, M. Optimal Process Design of Commercial-scale Amine-based CO2 Capture Plants. Ind. Eng. Chem. Res. 2014. DOI: 10.1021/ie5023767

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Summary of the Optimum Design Results for the Absorber and Stripper Columns

Coal: Illinois No. 6

(Supercritical)

Flue Gas Flowrate (kg/s) 821.26

Optimum Lean CO2 loading (mol/mol) 0.18‡

Optimum Liquid/Gas Ratio (kg/kg) 2.74‡

Absorber

Number of Absorber 2

Absorber Packing Mellapak 250Y

Diameter (m) 16.13

Optimum Height (m) 23.04

Stripper

Number of Stripper 1

Packing Mellapak 250Y

Diameter (m) 14.61

Optimum Height (m) 25.62

Specific Reboiler Duty (MJ/kg CO2) 3.69

‡A lean CO2 loading of 0.20 mol/mol with a liquid/gas ratio of 2.93 kg/kg is an alternative.

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Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS

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Optimum Lean CO2 Loading

0.14 0.16 0.18 0.20 0.22 0.24 0.26

560

570

580

590

600

610

620

630

640

650

660

670

680

690

700

0.14 0.16 0.18 0.20 0.22 0.24 0.26

26.5

27.0

27.5

28.0

28.5

29.0

29.5

30.0

30.5

31.0

Reboiler Duty (Illinois No. 6)

Reboiler Duty (Montana Rosebud)

Reboiler Duty (North Dakota)

Re

boile

r D

uty

(M

Wth)

Lean CO2 Loading (mol/mol)

2.40

2.60

2.80

3.00

3.20

3.40

3.60

3.80

4.00

L/G (Illinois No. 6)

L/G (Montana Rosebud)

L/G (North Dakota)

L/G

(kg/k

g)

with CO2 Capture & Compression (Illinois No. 6)

with CO2 Capture & Compression (Montana Rosebud)

with CO2 Capture & Compression (North Dakota)

with CO2 Capture only (Illinois No. 6)

with CO2 Capture only (Montana Rosebud)

with CO2 Capture only (North Dakota)

Ne

t P

lant

Eff

icie

ncy (

%)

Lean CO2 Loading (mol/mol)

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Optimum Lean CO2 Loading (Continuation)

0.14 0.16 0.18 0.20 0.22 0.24 0.26250

300

350

400

450

500

550

600

650

700

750

800

0.14 0.16 0.18 0.20 0.22 0.24 0.26500

550

600

650

700

750

800 Lean Pumps (Illinois No. 6)

Lean Pumps (Montana Rosebud)

Lean Pumps (North Dakota)

Rich Pumps (Illinois No. 6)

Rich Pumps (Montana Rosebud)

Rich Pumps (North Dakota)

Pu

mp

s D

uty

(kW

e)

Lean CO2 Loading (mol/mol)

Exchanger Duty (Illinois No. 6)

Exchanger Duty (Montana Rosebud)

Exchanger Duty (North Dakota)

L/R

He

at

Exch

an

ge

r D

uty

(M

Wth)

Lean CO2 Loading (mol/mol)

1.00x105

1.05x105

1.10x105

1.15x105

1.20x105

1.25x105

1.30x105

1.35x105

Exchanger Area (Illinois No. 6)

Exchanger Area (Montana Rosebud)

Exchanger Area (North Dakota)

L/R

He

at

Exch

an

ge

r A

rea

(m

2)

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Impact of Flue Gas Temperature on Performance

30 35 40 45 50 55 603.64

3.66

3.68

3.70

3.72

3.74

3.76

3.78

3.80

3.82

30 35 40 45 50 55 6086.5

87.0

87.5

88.0

88.5

89.0

89.5

90.0

90.5

91.0

Sp. Reb Duty (Illinois No. 6)

Sp. Reb Duty (Montana Rosebud)

Sp. Reb Duty (North Dakota)

Sp

. R

eb

Du

ty (

MJ/k

g C

O2)

Inlet Temperature of Flue Gas (oC)

400

450

500

550

600

650

700

750

Reboiler Duty (Illinois No. 6)

Reboiler Duty (Montana Rosebud)

Reboiler Duty (North Dakota)

Re

boile

r D

uty

(M

Wth)

CO2 Capture Efficiency (Illinois No. 6)

CO2 Capture Efficiency (Montana Rosebud)

CO2 Capture Efficiency (North Dakota)

CO

2 C

ap

ture

Eff

icie

ncy (

%)

Inlet Temperature of Flue Gas (oC)

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Impact of Lean Amine Temperature on Performance

30 35 40 45 50 55 603.6800

3.6805

3.6810

3.6815

3.6820

3.6825

3.6830

3.6835

3.6840

3.6845

3.6850

3.6855

3.6860

3.6865

3.6870

30 35 40 45 50 55 6089.98

90.00

90.02

90.04

90.06

90.08

90.10

90.12

Sp. Reb Duty (Illinois No. 6)

Sp. Reb Duty (Montana Rosebud)

Sp. Reb Duty (North Dakota)

Sp. R

eb D

uty

(M

J/k

g C

O2)

Inlet Temperature of Lean Amine (oC)

CO2 Capture Efficiency (Illinois No. 6)

CO2 Capture Efficiency (Montana Rosebud)

CO2 Capture Efficiency (North Dakota)

CO

2 C

aptu

re E

ffic

iency (

%)

Inlet Temperature of Lean Amine (oC)

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Impact of CO2 Capture Level

70 75 80 85 90 95 100

2.2

2.4

2.6

2.8

3.0

3.2

70 75 80 85 90 95 1003.60

3.62

3.64

3.66

3.68

3.70

3.72

3.74

3.76

L/G (Illinois No. 6)

L/G (Montana Rosebud)

L/G (North Dakota)

L/G

(kg/k

g)

CO2 Capture Level (%)

Sp. Reb Duty (Illinois No. 6)

Sp. Reb Duty (Montana Rosebud)

Sp. Reb Duty (North Dakota)

Sp

. R

eb

Duty

(M

J/k

g C

O2)

CO2 Capture Level (%)

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Summary: Overall Energy Performance

Illinois No. 6 Montana Rosebud

North Dakota

Fuel heat input, HHV (MWth) 1932.94 1932.94 1932.94

Steam turbine thermal input, (MWth) 1704.75 1704.75 1704.75 Steam turbine power, without steam extraction (MWe) 811.80 811.80 811.80

Steam turbine power, with steam extraction (MWe) 662.94 654.24 649.09

Power plant auxiliary loads (MWe) 11.44 12.12 12.57

Other auxiliary loads (MWe), estimated based on a US DOE report‡ 30.00 30.00 30.00

CO2 capture plant auxiliary loads (MWe) 19.72 20.15 20.42

CO2 Compression loads (MWe) 45.70 48.05 49.46

Power output without CO2 capture and compression (MWe) 767.36 767.36 767.36

Power output with CO2 capture only (MWe) 601.17 591.97 586.72

Power output with CO2 capture and compression (MWe) 555.48 543.92 536.64

Efficiency without CO2 capture and compression (%), HHV 39.70 39.70 39.70

Efficiency with CO2 capture only (%), HHV 31.10 30.60 30.30

Efficiency with CO2 capture and compression (%), HHV 28.73 28.12 27.74

‡US DOE "Cost and Performance Baseline for Fossil Energy Plants. Volume 1: Bituminous Coal and Natural Gas to Electricity," US Department of Energy, Revision 2, November 2010.

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Conclusions

The design of the CO2 capture plant can easily handle different coal types without operational issues. Fractional approach to flooding velocity was fairly constant. No flooding!

The performance order of the different types of coal investigated is as follows: Illinois No. 6 (bituminous) > Montana Rosebud (sub-bituminous) > North Dakota (lignite)

The Optimum lean CO2 loading lies between 0.18 and 0.22 for all the coal types investigated. A lean CO2 loading of 0.18 was adopted. 0.20 gave about the same performance!

The temperature of the lean MEA solution at the absorber inlet has minimal effect on the overall performance. There is no need to over-cool!

The flue gas temperature up to 45 oC has a very slight effect on the overall performance. However, its effect becomes slightly more pronounced above 45 oC. Do not over-cool!

Specific reboiler duty increases slightly with capture level up to about 90% and it increases sharply above 90%. The same L/G per CO2 capture level can be used for 75% to 90% CO2

capture level with minimal loss of performance. This is a plus for power plant flexibility!

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Energy Technology and Innovation Initiative (ETII) FACULTY OF ENGINEERING UNIVERSITY OF LEEDS