11.1.2 In addition to the information and plans required in Pt 5, Ch 24, 3 Information to be submitted, the following are
to be submitted for consideration:
- Details of the maximum and minimum ambient and sea water
temperatures within which the emissions abatement plant is designed to operate,
and maximum and minimum ambient air temperature and humidity where relevant,
i.e. where operation is temperature or humidity dependent.
- Details of the corrosivity of wash water for wet scrubbing
systems, e.g. specific gravity, temperature, pH, and presence of polluting
substances such as oil content and turbidity.
- The Pitting Resistance Equivalent Number (PREN) is to be
confirmed when stainless steels or nickel-based alloys are used for the wet
scrubbing system containing wash water.
- For scrubber towers, a Manufacturer’s Certificate for
materials and welding details including procedure.
- Details on storage and use of sodium bicarbonate powder used
in dry scrubbers, see
Pt 5, Ch 24, 10.2 Sodium bicarbonate.
11.1.5 The integrity of the weather deck is to be maintained. Where items of a scrubber
tower penetrate the weather deck and are intended to constitute the structural
barrier to prevent the ingress of water to spaces below the freeboard deck, their
structural strength is to be equivalent to the Rule requirements for this purpose.
Otherwise, such items are to be enclosed in superstructures or deckhouses fully
complying with the Rules.
11.1.6 Mounting arrangements are to take account of forces and moments generated at the
supports. Mounting arrangements are to take account of thermal expansion and
contraction.
11.1.7 Access is to be provided for inspection and checking of mountings,
fittings, controls and pressure-relief devices.
11.1.8 Closed loop wet scrubbers are to have natural gravity fall drainage from the wet sump
of the scrubber to the process tank or circulating pump suction, with the drain line
dimensioned to accommodate 125 per cent of the maximum pumping capacity of the
installed water pump(s). No valves are to be fitted to the drain line from the
scrubber sump to the process tank, unless it can be demonstrated that the
arrangements prevent the possibility of the scrubber filling with water and a
reverse flow into the engine exhaust duct. Where a valve is fitted to this line, the
system is to be protected as for the overboard discharge valve of an open loop
system, in accordance with Pt 5, Ch 24, 9.1 General 9.1.10.
11.1.9 For open loop wet scrubbers, the overboard discharge valve and any other
sea water valves downstream of the scrubber are to be protected in accordance with
Pt 5, Ch 24, 9.1 General 9.1.10. The sea suction valve(s) are
also to have position indicators which are to give remote indication of valve
position. The scrubber is to be mounted above the waterline under all operating
conditions to prevent seawater ingress into the scrubber from the natural flow.
11.1.10 In order to prevent the reverse flow of water into engines, boilers and
other machinery, wet scrubbing systems (open loop and closed loop) are to be fitted
with an overflow line. This overflow is to be dimensioned to accommodate 125 per
cent of maximum capacity of installed water pumps and is to have no impairment to
flow. This overflow line is to be directed to the process tank in closed loop or
hybrid installations and is to be directed overboard on open loop installations. The
overboard discharge is to have an effective means of preventing reverse flow of sea
water. Alternative arrangements to prevent the risk of reverse flow are subject to
special consideration.
11.1.11 Overboard discharge connections from scrubbers are to be positioned below the lowest
operating waterline and are to be internally protected from effluent-induced
corrosion.
11.1.13 Where a scrubber tower is installed or intended to be installed, attention is drawn
to the stability considerations and other applicable requirements of the National
Authority with whom the ship is registered.
11.1.14 The holding tanks for residues generated from the exhaust gas cleaning process are to
satisfy the following requirements:
- The tanks are to be independent from other tanks, except in cases where
these tanks are also used as the overflow tanks for chemical treatment
fluids storage tank.
- Tank capacities are to be decided in consideration of the number and kinds
of installed exhaust gas cleaning systems as well as the maximum number of
days between ports where residue can be discharged ashore. In the absence of
precise data, a figure of 30 days is to be used.
- Where residue tanks used in closed loop chemical treatment systems are also
used as the overflow tanks for chemical treatment fluid storage tanks, the
requirements for storage tanks apply.