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Unit of
Parameter MDA VT
Measure nary use of chemicals such as biocides, antifo-
Total Dry Weight 28 11 Ton aming and oxygen scavenger, the adoption of
membrane contactors implies only a periodical
Total Full Liquid Weight 40 13 Ton
cleaning by the Cleaning in Place (CIP) skid. The
Footprint 33 33 m 3 lower chemicals’ demand in membrane deae-
ration represents an important advantage since
Overall Volume 90 71 m 3 their supply is particularly critic in offshore in-
stallations.
Table 6. VT vs MDA: Plant size and weight On the other side, while the vacuum tower pa-
cking does not imply a frequent replacement, in
fact the plastic random packing could even last
all life, the membrane deaeration requires a re-
placement of the membranes.
The lower volume and the high modularity of the
MDA allow an easier installation. On the contra-
ry, in case of VT, a more complex assembly and
interconnection between different platforms’
desks is required. At last the heavier VT’s im-
pact on offshore structures imply more critical
mechanical constrains as, for instance, to their
own static action, waves motions has to be con-
sidered properly.

4.3 CAPEX and OPEX analysis
The economical comparison between membrane
deaeration and vacuum tower based project was
made in terms of both CAPEX (capital expenditure)
and OPEX (operating expenditure).
For capex evaluation, different contributions were
taken into account: the equipment, the instruments
Figure 5. 3D Model of Membrane deaeration system and the valves (Table 8). Equipment costs
included the deaeration systems (the vacuum
towers and the membrane contactors) plus the
internals and packing and the skids for chemicals
and/or cleaning. In addition, for capex evaluation,
also the vacuum generating system (including the
liquid ring vacuum pumps and the ejector) as well
as Nitrogen generation and purification system (to
reach a final Nitrogen purity equal to 99.99%) were
considered.
Dual media filters pretreatment contribution (and
all the other common equipment) was not included
in capex evaluation since the pretreatment was
common for the vacuum towers and membrane
deaeration. Similarly, the cost of the two feeding
pumps to the Dual Media filters, was not taken into
account being a common contribution for MDA
and VT.
The calculation of OPEX was made by considering
the contribution of feeding power costs, the
chemicals and consumables associated to both
the processes (Table 9). For electrical feeding
power costs, the adsorbed power of all the
pumps (dosing pumps, booster pumps) and of the
Figure 6. 3D Model of Vacuum Tower system control panel unit was considered. Moreover the
contribution of the chemicals was also included:
two deaeration systems, also an analysis was for the VT process the biocide I, the biocide
made in terms of plant management and mainte- II, the antifoaming and the oxygen scavenger
nance (Table 7). Regarding the chemicals, while consumption were considered. In the case of
the adoption of vacuum towers implies the ordi- membrane deaeration, only the contribution of the

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