1. Introduction - Firenze University Press

Net efficiency (%) 40.28 30.29 26.40
Efficiency penalty(%-points) - 9.99 13.88
As is shown in Table 3, due to the fact that Case 1 and Case 2 adopt the same MEA CO2 capture
process illustrated in the same Base Case, the process configuration and several basic parameters of
these two cases are similar to each other, such as coal input rate, reboiler heat duty, CO2 capture
amount and CO2 compression work.
However, because of the difference of the two capture cases in the extracted locations, the flow rate
and the parameters of extraction steam, the great differences lie in the power output of steam
turbine, net power output and net efficiency. In fact, on account of the high extraction pressure and
large power loss of IP cylinder after steam extraction in Case 2, its steam turbine output is only
461.57MW, 55.52MW less than that of Case 1, which in turn leads to the obvious drop of net power
output and net efficiency of Case 2 when compared with Case 1. Eventually, efficiency penalty of
Case 2 reaches 13.88% points, nearly 4% points higher than that of Case 1.
Though performance of Case 2 seems worse, more attention are paid to the production process of
power station in this case, which is closer to the practice. In fact, even for a newly-built power
station, the same constraints in CO2 capture process will be confronted if it uses the traditional
station design. In other words, in terms of a practical pulverised coal power plant which adopts the
chemical absorption method to achieve large-scale decarbonisation, the practical efficiency penalty
will be much higher than the theoretical analysis if no specific optimization is made.
In a word, specific optimization in the retrot scheme for CO2 capture in a pulverised coal power
plants will be very helpful to control the penalty of CO2 capture at a low level, which will be
discussed in the following section.
4. Special integration for CO2 capture in existing power plant
4.1. Add a new letdown steam turbine generator (LSTG)
Since the steam pressure of the IP-LP crossover pipe (9.32bar) are much higher than the required
steam pressure for solvent regeneration (about 2.1bar), a new letdown steam turbine generator is
proposed to utilize the surplus pressure for power generation, as is shown in Fig. 9.
Fig. 9. The structure of adding a new letdown steam turbine generator
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