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efficiency. Since teCmOp2 ecrraittiucrael, temperature is close High efficiency
to the ambient this fluid is strongly
Since the working fluid is at its supercritical state,
interesting for gas turbine power cycle applications. the work required to compress it decreases, with
The idea onfewus, igngoinsgupbearcckrittioca6l0Cs Oof2 as working the consequent enhanced efficiency. Referring
fluid is not the previous
to semi-closed configurations with internal oxy-
century, when researchers were looking for new combustion, also with turbine inlet temperature
ways of improving the thermodynamic efficiency of (TIT) lower than 1273 K, the thermodynamic
closed Brayton-Joule power cycles [9]. Nowadays, efficiency (LHV basis) is greater than 50%, including
such a technology could be exploited in different panredssuorxeygleonssepsr,odCuOct2ioncapfrtoumre implementation
state-of-the-art
applications and sectors (power, oil & gas,
transport). air separation units. Apart by increasing the
turbine inlet temperature, the efficiency is also
• It can be used to develop near-zero emissions going to increase if advanced oxygen production
and more load-flexible and compact gas
turbine back-up power plants (to match with processes are developed and implemented
non-programmable renewables).
instead of conventional air separation units.
Cost reduction
• It can becyacdleaspteudsin(sgemoi-xcylo-csoemd bSu-sCtiOon2 gas Tisdeheqeaulseostpoterarreatiatoilnnizg,eeapnr“hepasinpscueerliendse-oroielfaodSry-”gCaCOsO2 r2ecscytorcevlaeemsry,(afoorerr
turbine as
internal heat source) to continuously work
at its base-load with high efficiency (> 50%), other applications) without any other compression
including a highly integrated and cost effective system; hence, the CpOla2ntc,awpthuoresedolaeysountotiswkeeigpht
on the cost of the
CefOfic2iecnatplytucreonsttrroaltetghye, and with the ability to
partial load operation “quite simple” without any steam power section
by lowering both the fuel mass flow rate and (heat recovery steam generator and steam
operative pressures. It is remarkable to note turbine) compared to a CCGT plant.
that partial load operations are not any longer
related to environment constrains; hence, the Huge compactness
system is more efficient and flexible also at uTphetSo -ConOe2 high density makes the plant footprint
hundredth of that of a conventional
partial loads.
plant with the same power. Comparisons between
• It can be easily adapted to fruitfully use external the power sections of a state of the art USC
heat sources including Waste Heat Recovery
(WHR) applications. For example, it can be athnedrmoof daynSa-mCiOc 2 cycles, evaluated at the same
used in nuclear, Concentrated Solar Power conditions, highlighted that the
(CSP) and geothermal plants to increase their
efficiency or it can replace the steam section hSi-gChOer2 cycle power density (PD) was 250 times
of present designs of Combined Cycle Gas than USC, being PD (MW/m3) the ratio
Turbine plants to improve their load-flexibility
and efficiency (as known, the steam power between the net power and the working fluid
section makes the whole CCGT plant scarcely
load-flexible). volume evaluated at the condenser inlet section
Closed and semi-closed Brayton-Joule or
Rankine cycle configurations can be designed: [im10p]l.emS-eCnOtin2 gpothweemr plant compactness suggests
semi-closed configurations using (internal) in a distributed fashion closer
oxy-combustion of natural gas or hydrogen
as the high temperature heat source, suitable to population for electrical grid back-up.
for back-up power plant applications; closed
cycle configurations, obtained by replacing High load-flexibility
the oxy-combustor with a heat exchanger,
suitable for external heat sources applications. The absence of both tpheowCeOr2 capture facilities and
Characteristics of such a plant are: the steam recovery section, coupled to
the power plant compactness, are the strongest
motivations that justify the expected load flexibility
othfeS-a-CrtOp2owpoewr pelranctyscleeqsuwipipthedrewspithecCt CtoS.state-of-
It is finally observed that although the complexity
oafffortdhaebles,yssitnecmese,xisSt-inCgOp2ropvelannpt owteecrhgneonloegraytioins
equipment can be adopted. Special attention and
Near-zero emission development are required for specific devices,
Internal oxy-combustion of natural gas has
cbihduyyedrarcreloolyngnteCdneOs)ne2spaaaasntriaodptnirHo,on2daOunucd(notsiCnt;,lOyHw2H2Oic2tOhaopmiutnutarcyeaadnsbeybeyoaefadxbdtsruiaitrmicnotipnenaldgel such as the high-pressure oxy-combustor
capture facility and with very low parasitic energy
demand. (working with hydrogen or syngas is even more
challenging), the water separation unit and heat
exchangers, that have to be flexible. Special
attention and development are also required
for specific processes, such as the purification
of hot combustion gases, for the identification
Impiantistica Italiana - Settembre-Ottobre 2015 43
