MARITIME

EMISSIONS UPDATE
the system will eventually stop scrubbing.
To avoid that excessive buildup, a
closed loop system incorporates a small
continuous bleed (a slip stream) from the
circulation loop. That stream is continuously
replaced by fresh water to keep the
system in balance. Additional fresh water
is also added to replace the water that
is evaporated by contact with the hot exhaust
gas. Since the untreated discharge
water from a closed loop system has
much higher pollutant content due to the
normal build-up that occurs in the closed
circulation, additional water cleaning
equipment is required prior to discharge
at sea. The typical water cleaning equipment
used in closed loop operation is a
centrifuge or some type of positive filtration.
As with the open loop system, the
closed loop system will also include all
monitoring and control equipment. Additionally,
it will require caustic storage
and feed system as well as purge water
storage tank if desired. One major advantage
of a closed loop system is that
is can be constructed of typical stainless
materials because the pH levels are
easily controlled by caustic. Of course
chloride levels may affect the ability to
use stainless steel materials and therefore
a proper review of the water and
caustic used is required to make sure that
the maximum chloride levels are not exceeded
in the circulating solution.
The Hybrid Design
A hybrid design is a combination of an
open lop and a closed loop system. As
such a hybrid scrubber will be the most
expensive but the most flexible solution.
A hybrid system will have all the additional
equipment associate with a closed
loop system but will also circulate more
water and be constructed of higher grade
alloys as the open loop system (because
of the use of seawater in open loop operation).
The advantage of a hybrid system is
that it can be switched from open loop to
closed loop operation on command. One
can operate in closed loop mode when
in port of fresh water and then switch to
open loop when in open seas. This will
minimize the amount of caustic used and
in long run save operating money. Each
ship with a hybrid scrubber installation
will be able to optimize their operation
based on route and local port state requirements.
Stack Monitoring Equipment
The stack emissions are monitored by
a Continuous Emission Monitoring system
(CEM). The CEM sensor is located
in the stack above the scrubber unit. The
CEM unit will measure SO2 and CO2.
The emission data collected by this unit
is displayed on the CEM control panel
screen. The exhaust gas emission data
is also archived in the CEM panel along
with the wash-water monitoring data
(PAH, pH and turbidity) and the ship
GPS.
Water Monitoring Equipment
Per the IMO guideline for exhaust
gas cleaning systems, the effluent water
from the scrubber shall be monitored for
pH, turbidity, and PAH. The data collected
by these sensors is displayed on
the wash-water monitoring control panel
screen and is also archived on the CEM
control panel. Since IMO has set the turbidity
and PAH as increased levels from
the normal surrounding waters, it may
be a good precaution to install turbidity
and PAH monitors on the water intake as
well as the water discharge points to better
define the differential between inlet
and outlet. This may be very useful in
proving compliance even when the normal
water intake levels of turbidity and
PAH exceed the required IMO established
values.
Conclusion
Scrubbers work. Many scrubbers are
now in operation and many others in design
and installation phases. Because
of this initial problem some suppliers,
the Exhaust Gas Cleaning Systems Association
(EGCSA) was established and
all members vowed to a very strict code
of ethics. EGCSA member companies
work very hard at maintaining a high
standard of design and reputable sales
and marketing approach. Additionally
they are supporting the shipping industry
in working with IMO in clarifying
and simplifying some of IMO’s requirements.
All EGCSA member companies have
presently provided scrubbers to the shipping
industry and have had significant
successes. As an example, CR Ocean
Engineering (CROE) has several on
board units in successful operation and
many others in the design and fabrication
stage for some very reputable
shipping/cruising companies. Having
had more than 60 years of successful
scrubbing systems design under its belt,
CROE’s success in the marine industry
started with it’s first installations on a
Great Lakes bulk carrier.
The moral of the story is that scrubbing
systems can save significant money
if a ship operates in an ECA for more
than about 40 % of the time. Risks can
be managed by contracting with a known
and reputable company with proven
scrubbing system design experience (using
EGCSA member companies is one
way to minimize risk). In the end all
parties want a successful system operation
for many decades and all can benefit
by this IMO established equivalency.
D E S I G N
A S S E S S E D
22 Maritime Reporter & Engineering News • SEPTEMBER 2015