Institute of Energy Systems Prof. Dr.-Ing. A. Kather Dipl.-Ing. Sören Ehlers Jan Mletzko, M.Sc....

Institute of Energy Systems

Prof. Dr.-Ing. A. Kather

Dipl.-Ing. Sören Ehlers

Jan Mletzko, M.Sc.

Comparison of natural gas combined cycle power plants

with post combustion and oxyfuel technology at

different CO2 capture rates

The 8th Trondheim Conference on Capture, Transport and Storage, Trondheim, 16th-18th June 2015

TCCS-8Trondheim, 16th-18th June 2015

Institute of Energy SystemsGuD-POXY project

· NGCC (GuD) power plants with Post combustion and OXYfuel

· Hamburg University of Technology – Institute of Energy Systems

▸ Overall process simulation for post-combustion and oxyfuel

· University of the Federal Armed Forces Hamburg (Helmut-Schmidt-University) – Laboratory of Turbomachinery

▸ Investigation of turbomachinery

▸ Combustion experiments

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Project partners


Institute of Energy SystemsMotivation

· NGCC power plants have the lowest specific CO2 emissions of fossil

fuelled power plants

▸ ~ 340 g CO2 / kWhel (60 % net efficiency)

▸ Further reduction to << 100 g CO2 / kWhel with CCS technologies

· Studies of different capture processes assume different capture rates

▸ 90 % for post combustion / 100 % for Oxyfuel

▸ Net efficiency does not provide a common basis for comparison

· Legislative framework could favour the focus on a CO2 emission limit

▸ A limit of 100 g CO2 / kWhel requires 90 % capture rate for coal but only 75

% for natural gas

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Aim: Comparison of two NGCC options with post combustion and oxyfuel regarding the loss of electricity related to the amount of CO2 captured!


Institute of Energy SystemsReference plant

· Conventional NGCC power plant is taken as the reference plant for all processes of the project

· 2x ALSTOM GT26 with HRSG 1x steam turbine

▸ Triple pressure reheat steam cycle

▸ Once-through evaporator for the HP level

▸ Net power: 876 MW

▸ Gross/net efficiency: 59.8 % / 59.2 %

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GHPSH

CPH

IPE1

HPB

IPSH

LPB

RH

IPB

IPE2HPE1HPE2HPE3

Air

EV SEV

Pressure levels (HP/IP/LP): 159 bar / 40 bar / 4.2 barLive steam/reheat temperature: 585 °C


Institute of Energy SystemsPost combustion capture for NGCC

· Basic 30 wt.-% MEA capture unit (15 m absorber height)

▸ Steam extracted from crossover between the IP and LP steam turbine

▸ 90% capture rate in the base case

▸ CO2 compression to 110 bar

· Base case net efficiency 52.1 % (-7.1 %-pts.)

▸ Steam extraction

4.6 %-pts.

▸ CO2 compression

1.6 %-pts.

▸ Additional auxiliary duty 0.9 %-pts.

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0

1

2

3

4

5

6

7

8

9

10

3

3,5

4

4,5

5

5,5

6

0,6 0,7 0,8 0,9 1

Ove

rall

effici

ency

pen

alty

in %

-poi

nts

Spec

ific

heat

dut

y in

MJ/

kg C

O2

CO2 Capture rate

Specific heat dutyOverall efficiency penalty

Influence of the capture rate on the PCC unit

· Specific heat duty increases sharply at capture rates above 85 %

▸ Efficiency penalty varies between 4.8 and 9.4 %-pts.

· Same tendency for improved capture processes

▸ flue gas recycle shifts the sharp increase of the specific heat duty to higher capture rates (~ 90 %)

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L/G adjusted to the lowest specific heat duty for each capture rate


Institute of Energy SystemsNGCC with Oxyfuel

· Semi-closed oxyfuel combustion combined cycle (SCOC-CC)

▸ Pressure ratio of 60 due to sequential combustion

▸ O2 purity 95 vol.-% (0.202 kWh/kg O2), 3 vol.-% O2 (dry) in the flue gas

▸ 100 % CO2 capture Compression of the flue gas to 110 bar

▸ CO2 purity of 86.5 vol.-% (dry)

GEV SEV

O2 Fuel

HRSG

Cond

. 40°C

WaterCO2

110 bar

· Base case net efficiency 50.3 % (-8.9 %-pts.)

▸ O2 production 5.9 %-pts.

▸ CO2 compression 2.3 %-pts.

▸ Additional auxiliary duty 0.3 %-pts.

▸ Thermodynamics of the process 0.4 %-pts.

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Institute of Energy SystemsInfluence of the capture rate on the SCOC-CC

· Assumed CO2 purity for transport and storage 96 vol.-% (dry)

▸ CO2 purification (partial condensation) Reduced capture rate

▸ Two condensation stages at -25 °C and -30 – -50 °C

▸ Only small effects ASU loss independent of the capture rate

· Alternative: High purity O2, 1 vol.-% O2 (dry) in flue gas

▸ Energy demand for the ASU (99.5 vol.-% O2): 0.241 kWh/ kg O2

▸ 100 % Capture rate Additional penalty 0.8 %-pts.

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Institute of Energy SystemsSpecific electric loss

· Post combustion capture for natural gas has a significantly lower loss for a wide range of capture ratios Minimum at ~ 80 %

· SCOC-CC only advantageous if full capture is required

▸ If purity is restricted high purity oxygen is necessary

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0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.6 0.7 0.8 0.9 1

Sp

ecif

ic e

lect

ric

loss

in k

Wh

/kg

CO

2

CO2 capture rate

NGCC+PCC

SCOC-CC (95% O2+GPU)

SCOC-CC (99.5% O2 fullcapture)

SCOC-CCBase case Purity not sufficient

captured

refnetL

,

Coal-fired plants (90% CR)0.26 – 0.36 kWh/kg CO2


Institute of Energy SystemsConclusion

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· Post combustion capture for NGCC allows an adjustment of the capture rate to a required CO2 emission limit for a wide range of capture rates

▸ Specific electric loss is approx. constant from 60 to 90 % at 0.38 kWh/kg CO2

▸ Sharp increase of the specific electric loss for higher capture rates

▸ Minimum specific loss at 80 % capture rate

· The SCOC-CC leads to a higher specific electric loss of > 0.45 kWh/kg CO2

▸ Specific loss increases for lower capture rates because the ASU is independent of the capture rate

▸ Only at full capture case advantageous compared to post-combustion capture

▸ 96 vol.-% CO2 purity at full capture is only achievable with high purity oxygen

· Compared to coal-fired plants the specific electric loss due to CCS technologies is higher for NGCC plants



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Thank you for your attention!Questions?

Institute of Energy Systems Prof. Dr.-Ing. A. Kather Dipl.-Ing. Sören Ehlers Jan Mletzko, M.Sc....

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Transcript of Institute of Energy Systems Prof. Dr.-Ing. A. Kather Dipl.-Ing. Sören Ehlers Jan Mletzko, M.Sc....