1. Introduction - Firenze University Press

There are currently studies carried out on new types of sorbents in order to decrease their
regeneration heat consumption (i.e. for MEA from 4,5 MJ/kg CO2 to 3 MJ/kg [2]). Because of large
amount of steam required it is only possible to extract it from IP to LP line. Thermal parameters at
this point should fulfill sorbents regeneration process requirements and on the other hand be low
enough to avoid thermal degeneration of the sorbent. The desired pressure should be then equal to
p=ps(T+Ts)/(1- )
Where: T – Sorbent upper temperature, Ts – upper temperature difference, – pressure loss
coefficient.
If one decides to use amine sorbents, then it is necessary to heat them to ca. T = 127 °C. If Ts = 5
K and = 0.02, then steam of pressure p = 0.3 MPa is needed to feed the sorption unit.
2.5. Results of the design calculations.
It was assumed in computations that the plants nominal working conditions is pure condensation,
which means no steam is provided for district heating. Table 2 shows calculated results for
considered variants of nominal electric power of 305 MW each. Computations were carried out
under assumption that the house load is equal to 7.5 % of plants gross power. They were also
performed for two values of sorbents heat consumption.
Table 2. Results of design calculations
Only condensation With CC unit steam
consumption
Fresh steam flow rate, kg/s 209 245,2 231,5
Sorbents energy consumption,
MJ/kgCO2
- 3,89 2,83
CO2 separation steam flow
rate, kg/s
0 101,3 70,298
Steam feeding LP turbine flow 140,12 69,48 90,916
rate, kg/s
Cycle efficiency, % 51,23 43,48 46,14
Gross cycle efficiency, % 49,35 42,09 44,59
Net cycle efficiency, % 45,65 38,94 41,24
Boiler efficiency, % 94,41 94,41 94,41
Heat rate, kJ/kWh 6886,6 8074,1 7711,8
Fuel flow rate, kg/s 26,87 31,524 30,06
CO2 flow rate, kg/s 59,398 69,686 65,793
Percentage of removed CO2,
%
0 90 90
Steam mass flow rate produced in boiler depends on the chosen variant. In case of a “capure-ready”
CHP plant it is smaller than that in case of a plant already equipped with a CC installation. It is
related to the bigger mass flow rate through LP turbine compared to that in the previous case, which
is responsible for generating more mechanical power. Sorbents heat consumption has high impact
on work indices of a CHP plant that is already build with a CCS installation. Its reduction by 1
MJ/kgCO2 causes an efficiency growth of 2% points. Whereas in case of “capture-ready” plant the
efficiency is higher by 4.5 % points compared to a plat with CC unit of sorbents energy
consumption equal to 2.83 MJ/kgCO2 and about 6.5 % points of sorbents energy consumption
equal to 3.89 MJ/kgCO2. Calculations included only sorbents energy needs and left out sorbent
pump losses and CO2 compressors work.
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