Design Challenges

In a fossil steam or combined cycle power plant, the steam's primary function is to drive a turbine to generate electrical power. However in a carbon capture plant, steam

Table 10.1 Technology requirements for possible future power generation options3

2008:

No CO2 separation

Future: with CO2 separation1' (coal feedstock)

SCPC

NGCC

IGCC

IGCC

SCPC

Oxy-Fuel

Chemical looping

Efficiency, %, LHV

42-44

58%+

40-42

30-35

30-35

40-45

50-75%

Gasifier

No

No

Yes

Yes

No

Yes

No

ASU for oxygen

No

No

Yes

Yes

No

Yes

No

Solvent recovery

No

No

No

Yes

Yes

No

No

of CO2

a Efficiencies derived from various sources [1, 4, 7, 11]

b The term "separation" is used as opposed to capture to indicate that the CO2 can be isolated from the other flow streams. Compression not included a Efficiencies derived from various sources [1, 4, 7, 11]

b The term "separation" is used as opposed to capture to indicate that the CO2 can be isolated from the other flow streams. Compression not included will also be siphoned away to regenerate the solvent, separating the CO2 as a gas (although at much higher concentration than it was extracted from the exhaust gas). Most of the energy penalty is "paid-for" with low-pressure steam. Steam that should be used to generate electricity is instead sent to regenerate solvent. This situation creates a major design quandary: If the steam turbine is designed to handle the smaller fraction of the total flow (because some will be shifted to the regeneration loop), what happens to the steam when the carbon capture system shuts down? Is it vented to atmosphere or by-passed and sent to a condenser? If so, should the condenser be sized to handle additional steam in case of a failure, a feature that makes the plant that much more expensive. Another option is to design the turbine to handle the occasional additional steam flow and a larger capacity generator. This scenario implies that both a larger steam turbine and generator would be installed, but operated at reduced load while the regenerator is in operation. This too adds to the cost of the plant and the ultimate cost to the consumer.

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