buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 4, 2012 13
Making thermodynamic analysis it is useful to analyse some details:
The regasification process using Open Rack technology is fully
dissipative, moreover cold is released in the sea near the regasification site and
it gives rise to environmental problems.
Some other regasification technologies (e.g.: Fired heaters with
water/intermediate fluid, Submerged combustion vaporizers, CHP Plants) use a
lot of LNG vaporized, although in improved CHP Plants (e.g.: Dispenza et al.,
2009 a-b) a considerable cold exergy recovery there is, this improves
noteworthy the plant performance.
The modular unit proposed don’t use heat produced burning LNG
regasified, moreover it allows to recovery cold physical exergy to be used in a
lot of various processes and the regasification process reaches a suitable
thermodynamic performance reducing process irreversibility.
The use of CO2 as a secondary cold transfer fluid requires the study of
innovative systems into which dissipative service cycles are used, these are
based on the concept of: pumping CO2 in liquid phase, transfer of CO2 in liquid
phase to end users, use of CO2 in liquid phase evaporators to end users to
delivery cold available for refrigeration processes, transfer of CO2 in gaseous
phase returning it to regasification site.
The exergy of LNG and of NG considered in the Thermodynamic
analysis is the Physical Exergy. Actually, all processes which evolve in the
Modular Unity proposed (Dispenza et al., 2009 c) don’t include burning of
LNG regasified. The input exergy of LNG to be regasified include the physical
exergy of cold and the physical exergy due to pumping LNG in liquid phase.
The output exergy of NG is its physical exergy. The Dead State considered is a
Restricted Dead State: the fixed quantity of matter under consideration is
imagined to be sealed in an envelope impervious to mass flow, at zero velocity
and elevation relative to coordinates in the environment, and at the temperature
T0 and pressure P0. Thermodynamic analysis includes both Energy and Exergy
analysis. A methodology has been built, duly defining each parameter included
in the detailed analysis reported below (Nomenclature). Main results obtained
derived by numerical simulation using the model derived at DREAM (Dispenza
et al., 2009 c) are reported later.
For sake of clearness some results of Exergy analysis are shown later in
Fig. 8 in graphical format (Sankey Diagrams).
3.6. Energy and Exergy Efficiency of the Modular Unit
In the plant working with Ethane cold is delivered to a secondary fluid or
a cooling process in the heat exchangers CU, KE1, KE2, KE3 (Fig. 2).
At the same time Ethane is heated and it vaporizes. The cold duty of each
device composes the whole cold duty for this part of the regasification facility.