How to determine vessel emissions
A step by step guide
Your vessel is unique. It therefore goes without saying that your emissions will deviate (slightly) from what is stated by IMO, in particular with regards to NOx. That is why we have written an elaborate how-to-guide in which we explain in more detail our methodology and the physics behind combustion and emissions. Contact the helpdesk for clarification.
+ Step 1. Determine fuel consumption
The first step is to determine the type of fuel that is used, and the fuel consumption of your vessel in metric tons. For most shipowners, fuel type and consumption can be taken from daily progress reports or bunker fuel notes.
In case only the volume of fuel is known to you, weight can be determined by multiplying the volume times the density of the fuel type. For example, 1 m3 of MDO equals 0.89 metric tons of MDO.
+ Step 2. Determine emission factors
Each type of fuel has associated emissions, the most important being CO2, NOX, SOX, PM (Particulate Matter) and CH4. The table below shows the amount of emissions in kilograms when 1 metric ton of fuel is burned (source: IMO Greenhouse Gas Study 2020 table 53). With fuel consumption and emission factors known, you can now calculate emissions. *The averages of IMO GHG Study 2020 have been taken [kg/mT].
+ Step 3. Calculate emissions
You can determine emissions by using the following equation:
Emission [kg] = Fuel Consumption [mT] x Emission Factor [kg/mT fuel]
Example (1) Larry has a crane vessel called Crany McCraneface that consumes 10 metric tons of MGO per day. He wants to know the carbon footprint of Crany McCraneface. Table 2 shows him that the emission factor of CO2 for MDO is 3206, resulting in 32,060 kilograms of CO2 emissions per day, or 32.06 metric tons.
Example (2) Mary has an LNG tanker called Tanky McTankface that consumes 10 cubic meters of LNG per day. She would like to know the CO2 and CH4 emissions. Table 2 shows her that the emission factors of LNG for CO2 and CH4 are 2750 and 8.27 respectively, resulting in 27,500 kilograms of CO2 and 82.7 kilograms of CH4 per day.
+ References
IMO - Fourth IMO Greenhouse Gas Study 2020
IMO – MEPC.281(70)
ISO 8217 – Fuel standard for marine fuels
+ Disclaimer
It is assumed that for this guide, the reader is equipped with general knowledge on offshore and maritime industry, power generation on-board vessels and emission calculation methodology. Always take good care in verifying the emissions yourself, we cannot guarantee the outcome for individual and specifically unique calculations. No rights can be derived from this information.
Engine Settings affect emission factor (!)
It should be noted that these emission factors are (in some cases) heavily influence by engine settings. In the case with NOx for example, the amount of emissions can vary significantly. The variation for CO2 is much less and is primarily based on the carbon content of the fuel. Another factor to be taken into account, is methane slip for LNG engines, which could increase carbon equivalent footprint. In order to effectively and truly measure emissions, it is advised to install a continuous emissions monitoring system (CEMS).