INTERNATIONAL MARITIME ORGANIZATION
E
IMO
SUB-COMMITTEE ON BULK LIQUIDS
AND GASES
12th session
Agenda item 6
BLG 12/6/11
30 November 2007
Original: ENGLISH
REVIEW OF MARPOL ANNEX VI AND THE NOx TECHNICAL CODE
Proposal for amendments to the Guidelines for on-board exhaust gas-SOx
cleaning systems
Submitted by Finland
SUMMARY
Executive summary:
This document provides comments and proposals for consideration
for finalizing the Guidelines for on-board exhaust gas-SOx cleaning
systems – MARPOL Annex VI, regulation 14(4)(b), as developed by
the second Intersessional Meeting of the BLG Working Group on Air
Pollution
Action to be taken:
Paragraph 3
Related document:
BLG 12/6/Add.1
1
Annex 6 of BLG 12/6/Add.1 contains draft Amended Guidelines for Exhaust Gas
Cleaning Systems – MARPOL Annex VI, regulation 14(4)(b), prepared by the second
Intersessional Meeting of the BLG Working Group on Air Pollution. Finland has considered the
draft Amended Guidelines and found some issues which should be revisited by BLG 12.
2
The comments are related to paragraph 10.1.5.1 of the draft Amended Guidelines
concerning washwater criteria for nitrates, see annexes 1 and 2. Finland proposes that
paragraph 10.1.5.1 should be amended as follows, see the struck out and underlined text:
10.1.5.1 The washwater treatment system should prevent the discharge of nitrates beyond
that associated with a [10%][12%] removal of NOx from the diesel engine exhaust, or
beyond [1] [60] mg/l normalized for washwater discharge rate of 45 tons/MWh
whichever is greater.
Action requested of the Sub-Committee
3
The Sub-Committee is invited to consider the proposed amendments and decide as
appropriate.
***
For reasons of economy, this document is printed in a limited number. Delegates are
kindly asked to bring their copies to meetings and not to request additional copies.
I:\BLG\12\6-11.doc
BLG 12/6/11
ANNEX 1
THE COMMENTS AND PROPOSED AMENDMENTS TO SECTION 10.1.5.1 OF THE
DRAFT AMENDED GUIDELINES FOR EXHAUST GAS CLEANING SYSTEMS –
MARPOL ANNEX VI, REGULATION 14(4)(B)
#
1
Section
10.1.5.1
Proposed amendment
Comment 1:
Presently the information of NOx removal in scrubbers is very limited,
though it is believed to be typically clearly below 10%. This is indicated
by samples taken in the past, although also higher figures for NOx
removal have been encountered, up to 10%. Scrubbers are efficient in
removing NO2 but not efficient in removing NO. Of the exhaust gas from
a diesel engine typically about 95% is NO and 5% is NO2, but NOx
measurements of diesel engine exhaust gases show variations between
engine types. This ratio is temperature dependent, and exhaust gas boilers
may also contribute to converting NO to NO2. This could cause
unnecessary complications for design of environmentally friendly
energy-efficient machineries with efficient waste heat recovery. With the
nitrate clause the intention of the IMO is to address cleaning devices
designed to remove NOx, not to complicate the introduction of normal
SOx-scrubbers. To eliminate the uncertainty introduced by the 10% limit
it is proposed to increase it to 12%.
Proposal 1:
Replace the “10%” figure with “12%”.
2
3
10.1.5.1
10.1.5.1
Comment 2:
The possibility to have both an SCR and a SOx-scrubber in the same
exhaust gas system should be considered. The exhaust gases are always
conducted first to the SCR and then to the scrubber. A possible exhaust
gas boiler is installed between these devices. The SCR may well reduce
the original NOx-level by 90%, and removing, e.g., 15% of the remaining
10% (= 1.5% of original NOx from the diesel engine) should not be
considered as a violation of the scrubber washwater regulations. The
scenario of combining wet NOx-reduction methods in the diesel engine
with a SOx-scrubber should equally be considered, with a possible impact
on the NO/NO2 ratio. The nitrate limit in the scrubber washwater should
therefore reasonably refer to a percentage of the NOx-emission of the
diesel engine, not of the NOx in the scrubber inlet.
Proposal 2:
Insert the text “diesel engine” before the word “exhaust”.
Comment 3:
The nitrate concentration associated with a 10% NOx removal is 51 mg/l.
Considering comment 1 above referring to 12% NOx removal the figure
is 61 mg/l. Calculations are given in appendix 2.
Proposal 3:
Replace the “1 mg/l” figure with “60 mg/l”.
***
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BLG 12/6/11
ANNEX 2
CALCULATION OF NITRATE CONCENTRATION ASSOCIATED
WITH NOx REMOVAL
NOx in the exhaust gas
NO2/NOx
NO2 in the exhaust gas
N molecular mass
O molecular mass
NO2 molecular mass
N in the exhaust gas
Washwater flow
N in the washwater
NO3 molecular mass
Nitrates (NO3) in the washwater
g/kWh
%
g/kWh
g/mol
g/mol
g/mol
g/kWh
m3/MWh
mg/l
g/mol
mg/l
17
5
0,85
14
16
46
0,259
45
5,749
62
25,46
17
10
1,7
14
16
46
0,517
45
11,50
62
50,92
17
12
2,04
14
16
46
0,621
45
13,80
62
61,10
The following assumptions were made:
1.
NOx content in the exhaust gas (from 2-stroke engine) is assumed to be 17 g/kWh.
2.
NO2 portion of NOx is typically 5%.
3.
All NO2 in exhaust gas is dissolved in scrubber washwater.
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