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his paper aims at making an overall vacuum towers while higher opex are associated
comparison between two technolo- with MDA. Finally, weights and volumes were lower
gies for oxygen removal from injection in case of degassing by MDA than by VTs.
seawater in offshore platforms: vacu-
um towers and membrane deaeration.
TThe comparison was made between 1. Introduction
an executed vacuum towers based project (treating In many Oil & Gas offshore operations, the amount
an overall inlet water flow rate of 92.5 m /h com- of recovered oil from the reservoirs is increased by
3
ing from pretreated seawater) and the equivalent means of several engineered techniques: among
membrane deaeration (MDA) project configuration these, the injection of seawater into the wells plays
obtained by the replacement of the towers and its a very important role.
ancillaries with the membrane deaeration. The two Before being injected into the oil reservoirs, prelimi-
deaeration modules systems were compared in nary seawater treatments must be performed such
terms of the following characteristics: as the reduction of suspended/dissolved solids, di-
• Performance of deaeration treatments: mea- spersed oil and dissolved gases. Oxygen, carbon
sured in terms of oxygen concentration in the dioxide and hydrogen sulfide are the dissolved ga-
outlet treated water stream; ses frequently found in injection water. In particular,
• Equipment configuration: the configuration the content of oxygen must be reduced in order to
of both systems including all the valves/in- avoid such problems of corrosion and biogrowth
struments and the service equipment were which may affect the integrity of the reservoir.
analyzed; A conventional approach for oxygen removal from
• Costs evaluation: Both Capital costs (CAPEX) injection water is the utilization of vacuum tower re-
and Operative costs (OPEX) associated with moving other than oxygen, carbon dioxide and all
the two systems were evaluated; the other dissolved gases.
• General characteristics: Footprint and weights, In a vacuum tower the reduction of gases is carried
Chemicals consumption, systems’ operability out by reducing system pressure and consequently
and transportation. gases solubility in agreement with the Henry Law;
The results showed that for the specific case taken the gases which are separated from the water are
into consideration, higher performances can be vented from the deaerator.
reached by membrane deaeration system: in fact This approach presents many limits one of them
an outlet oxygen concentration lower than 10 ppb is the low performance in the oxygen reduction: in
was reached by membrane deaeration while higher many cases an outlet oxygen concentration lower
oxygen concentration (about 50 ppb) was reached than 50 ppb cannot be reached with the exclusive
by vacuum towers. In terms of costs, capex saving use of this treatment, so it is necessary the additio-
resulted by using membrane deaeration instead of nal supply of an oxygen scavenger.

Italian deletegates attending
the 10 th “Membrane
Technology for Climate
Change” workshop, in
Daejeon, Korea, June 21 st
-24 2017.
th
The event was organized
by Korea Research Institute
of Chemical Technology
(KRICT) with the collaboration
of the Italian Institute on
Membrane Technology (ITM-
CNR)

Impiantistica Italiana - Luglio-Agosto 2017 65