Third IMO Greenhouse Gas Study 2014

Inventories of emissions of GHGs and other relevant substances 103
vessels. Further information relating to the approaches used to estimate auxiliary engine loads are provided
in Section 1.2.5 and Annex 1. A detailed explanation of auxiliary engine power prediction can be found in
Starcrest (2013).
2.2.4 Boilers
Emissions from auxiliary boilers vary based on vessel class and operational mode. For example, tankers
typically have large steam plants powered by large boilers that supply steam to the cargo pumps and in some
cases heat cargoes. For most non-tanker class vessels, boilers are used to supply hot water to keep the main
engine(s) warm (during at-berth or anchorage calls) and for crew and other ancillary needs. These boilers are
typically smaller and are not used during open-ocean operations because of the waste heat recovery systems
(i.e. economizers) that take the waste head from the main engine(s). Unlike main and auxiliary engines, the
emissions factors do not change, as there are no regulatory frameworks associated with boilers. Of the three
emission source types, boilers typically have significantly fewer emissions than main and auxiliary engines.
Further details about auxiliary boilers are provided in Section 1.2.5 and Annex 1.
2.2.5 Operating modes
The auxiliary engine use profiles have been specifically defined for each ship type and size class. Furthermore,
auxiliary engine use varies according to vessel operating modes, which are defined by vessel speed ranges.
The modes used in this study are defined in Table 40. Auxiliary engine use during harbour visits is divided into
two modes: “at berth” describes the auxiliary engine use during cargo loading or unloading operations and
“anchoring” involves extended waiting periods when cargo operations do not take place.
Table 40 – Vessel operating modes used in this study
Speed
Mode
Less than 1 knot
At berth
1 knot–3 knots Anchored
Greater than 3 knots and less than 20% MCR Manoeuvring
Between 20% MCR and 65% MCR
Slow-steaming
Above 65% MCR
Normal cruising
Further details on auxiliary engine and boiler loads, by vessel class and mode, are given in Section 1.2.5 and
Annex 1.
2.2.6 Non-combustion emissions
Emissions from non-combustion sources (refrigerants and NMVOCs from oil transport) on board vessels were
evaluated with the top-down approach using the fleet-wide methodology described in Section 2.1.3 to maintain
consistency with the Second IMO GHG Study 2009. The emissions factors of non-combustion sources have
wide variations and the significance to overall GHG emissions is small (less than 3%). It is very unlikely that
the bottom-up approach to the modelling of non-combustion sources would change this conclusion.
Methane emissions
Emissions of CH 4 to the atmosphere are associated with LNG-powered vessels and include venting, leakage
and methane slip. Venting and leakage related to maritime LNG operations are not included in this report.
Methane slip during the combustion process is accounted for in the combustion emissions factors detailed in
Section 2.2.7.
NMVOC emissions from non-combustion sources
The NMVOC emissions from crude oil cargo operations and transport have not been included in the bottom-up
analysis. An estimate of global NMVOC emissions has been presented in the top-down analysis (see Section
2.1.3).