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1. Introduction - Firenze University Press

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N m<br />

eT<br />

4a<br />

<br />

~ T<br />

cp<br />

T4a<br />

1 ( K)<br />

iT <br />

mT<br />

T<br />

The gross electrical power of the air separation unit depends on the expander gross power ( N eT ),<br />

the compressor gross power ( N eK ) and the generator efficiency ( g ). The relationship between<br />

these quantities is as follows:<br />

N<br />

elTG<br />

N eT eK g<br />

N<br />

(5)<br />

Figure 4 shows a graph of boiler thermal efficiency as a function of oxygen recovery rate of the air<br />

separation unit. It should be noted that the boiler thermal efficiency increases from about 55% for<br />

low oxygen recovery rates to about 83% for high recovery rates. The boiler thermal efficiency<br />

depends on the live steam flow rate ( 6s m ), the reheated steam flow rate ( m 8s ), the enthalpy of live<br />

seam leaving the boiler ( 6s h ), the enthalpy of feed water at inlet to the boiler ( h 2s ), the enthalpy of<br />

reheated steam leaving the boiler ( h 8s ),the enthalpy of reheated steam at the inlet to the boiler ( h 7s ),<br />

the fuel mass flow rate ( 1c m ) and fuel lower heating value ( W dp ). The equation showing the<br />

relationship between these quantities can be written as:<br />

m 6s h6s<br />

h2<br />

s m<br />

8s h8s<br />

h7s<br />

<br />

k <br />

(6)<br />

m<br />

W<br />

Boiler thermal efficiency, %<br />

85<br />

80<br />

75<br />

70<br />

65<br />

60<br />

1c<br />

dp<br />

55<br />

40 45 50 55 60 65 70 75 80 85 90 95 100<br />

Oxygen recovery rate, %<br />

Fig.4. Thermal efficiency of the oxy type boiler as a function of the air separation unit oxygen<br />

recovery rate<br />

The thermal efficiency of steam cycle depends on the heat supplied to the steam cycle ( d Q ) and the<br />

heat discharged from the steam cycle ( w Q ).The relationship between these quantities is as follows:<br />

Q<br />

Q<br />

d w<br />

obp <br />

Q<br />

(7)<br />

d<br />

The gross efficiency of electricity generation is calculated in terms of the generator electrical power<br />

driven by the steam turbine. The electricity generated in other units is included in their auxiliary<br />

recovery rates. The gross efficiency of electricity generation depends on the steam turbine electrical<br />

power ( el<br />

256<br />

N ), the fuel flow rate ( 1c m ) and lower heating value ( W dp ).The equation showing the<br />

relationship between these quantities can be written as:<br />

(4)

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