Air Pollution is a serious threat for living organism. It causes health problems, agricultural problems and economic effects predominantly. Shipping is an unavoidable component regarding air pollution.
IMO (International Maritime Organization) introduced various regulations and code under MARPOL Annex VI to control the air borne pollution due to shipping.
Marine Engine Emission
Marine Diesel Engine is internal combustion engine in which low grade of fuels are used for combustion. Engine uses air, fuel and lube oil as input and produces work, heat and exhaust as output. Quality of fuel and process of combustion define the output of the engine. Combustion of low grade fuel causes serious environmental issue like Air Pollution, Ozone layer depletion etc. Simply, this exhaust gas is not eco-friendly.
Exhaust gas emission from marine diesel engine consists of Sulphur oxides, Nitrogen oxides, Carbon monoxide, Carbon dioxide, Hydrocarbons, Particulate matters, Soot, Smoke etc.
Remember: Emissions are subjected to Engines. There is nothing to do with ships. All efforts are made for Engines to control the emissions.
Sulphur oxides are famously known as SOx. The reason behind the emission of sulphur oxides from exhaust gas is the presence of sulphur in crude oil. Low grade fuel oil contains generally 3-5% sulphur. During combustion of fuel, sulphur is oxidized due to presence of air and high temperature. Sulphur dioxide and sulphur trioxide are formed due to oxidation of sulphur in a ratio of 15:1.
SOx reacts with water vapour and produces sulphuric acid. (SOx + H₂O → H₂SO₄)
Sulphuric acid also forms sulphides with other substances. These sulphides are nothing but a part of particulate matters.
Sulphur oxides are toxic in nature. It causes health problems like lung cancer, swelling etc. Photosynthesis is affected. Alkalinity of soil is also deteriorated due to sulphuric acid of acid rain.
Oxides of Nitrogen are famously known as NOx. Oxides of nitrogen are nitrous oxide (N₂O), nitric oxide (NO) and nitrogen oxide (NO₂). NO₂ and N₂O are formed in the ratio of 5:1. According to MEPC shipping shares more than 15% of the total NOx emission.
Major sources of nitrogen are: Presence of N₂ in air and Nitrates in fuel oil. At high temperature (combustion temperature), molecular nitrogen dissociates and reacts with oxygen to form oxides.
Note: Higher NOx formation is due to higher combustion temperature and slower speed.
Nitrous oxide is a dangerous green house gas. It’s hundred times bad as CO₂. Nitrogen oxide is a pollutant and major component of smog. It reacts with water and forms nitric acid. All these forms affect life and ecology of the earth very intensively. That’s why it is important to control the emission of NOx.
Oxides of carbon
Exhaust gas contains significant amount of oxides of carbon due to burning of hydrocarbon i.e. fuel oil. Carbon dioxide and Carbon monoxide are produced in combustion process. These oxides enhances green house effect and also named as green house gas. Also, emissions of CO, CO₂ and Hydrocarbon are low due to excellent thermal efficiency of the diesel engine cycle. We are going to discuss about Green House Effect, but to control the emission of CO₂, IMO (International Maritime Organization) emphasizing on indexes for all vessels. There are two famous indexes:
- EEDI = Energy Efficiency Design Index
- It is an index for designing a ship for desired CO₂ emission. Less EEDI indicates more energy efficient design.
- There are actual EEDI and required EEDI for comparison of energy efficiency. Required EEDI is a prescribed limit and actual EEDI is the energy efficiency (CO₂ emission in gram) per carried cargo (for certain mile and certain cargo). There are interesting mathematical formulas for calculating EEDI.
- It promotes the energy efficient machinery and engines at sea. Energy efficient machinery is nothing but less polluting machinery.
- MEPC (Marine Environment Protection Committee) mandates EEDI for all new ships design.
EEDI Technical File: It’s a document for the certification of EEDI.
- EEOI = Energy Efficiency Operational Indicator
- It’s a tool for monitoring the efficiency of ship for a given time.
- It indicates the fuel efficiency for the vessel.
Here another important plan enters i.e. SEEMP (Ship Energy Efficiency Management Plan). It’s a managerial plan for improving the energy efficiency economically. Later we’ll discuss about SEEMP in details.
Note: EEDI is mandatory for all new ships. And SEEMP is for all ships.
These are nothing but the suspended particles in exhaust gas which remains unburnt during combustion period. Lube oil is also a major factor except low grade fuel oil for generation of particulate matters because it does not burn completely. These particles have organic as well as inorganic material. Inorganic material doesn’t burn easily and remains unburnt. These particles pollute the environment.
CO₂ and CO emissions are obvious due to combustion of hydrocarbon product and CO₂ has excellent cycle in the nature, so CO₂ is less hazardous than NOx and SOx. IMO emphasizes more on the limitation of NOx and SOx emission as it is crucial for ecology.
Due to Process of Combustion
Due to Quality of fuel
To reduce NOx, Improve design of engine and Combustion
To reduce SOx, Improve fuel quality
Control over SOx Emission
- Shipping industry contributes more than 13% of total SOx emissions.
- Simply, SOx emissions can not be eliminated completely. But It can be reduced drastically.
- To minimize the SOx emissions, there are two ways: Use technology – (Treatment of exhaust gas) and Use good quality of fuel – (Fuel having very less sulphur content).
- Technology for reducing SOx is a good option for controlling SOx emissions but it can’t be enforced. Only one option that can be enforced to shipping i.e. fuel quality (less sulphur content fuel oil). And this is what IMO has enforced.
- There are two popular techniques for reducing the SOx emissions: Scrubber Technology and Sulphur Neutralization Technique
- Scrubber is nothing but a purifier. It is used for removing the SOx content from exhaust gas.
- There are 2 types of scrubber: Open Type & Closed Type.
- Open Type uses sea water and Closed Type uses fresh water for scrubbing the exhaust gas.
- Wartsilla is old player in scrubber technology and it claims 97% efficient for SOx removal.
- It uses fresh water with NaOH to make alkaline water. Alkaline water is sprayed into exhaust gas which absorbs SOx content and exhaust gas leaves without SOx.
- Finally fresh water is recirculated, treated and discharged into sea.
- No doubt, It’s costly.
Sulphur Neutralization Technique: In this technique, sulphur content is neutralised by lubricating oil. Proper cylinder lubrication neutralizes the sulphur and thus reduces the SOx emission. This is not as efficient as scrubber technology.
MARPOL Annex VI introduced 2 sets of requirement for SOx emissions: Global & Special.
Global requirement is valid for all ships throughout the world and special requirement is provided for some areas (SECAs) where rules are more stringent. See the table for limits, enforced by IMO:
Special Area Limits
4.5% m/m prior to 1 January 2012
3.5% m/m on and after 1 January 2012
0.5% m/m on and after 1 January 2020
1.5% m/m prior to 1 July 2010
1.0% m/m on and after 1 July 2010
0.10% m/m on and after 1 July 2015
What is Global Cap?
Global Cap is nothing but an upper limit of sulphur content in fuel oil that is allowed throughout the world. To reduce SOx emission, IMO introduced a cap (upper limit) of 4.5%/3.5%/0.5% sulphur content in fuel oil for ships. New global cap was introduced to use fuel oil with less than or equal to 0.5% m/m sulphur content. At present, global cap limit is 3.5% m/m. Here % m/m denotes % of mass per mass i.e.1 gm sulphur content is present in 1000 gm of fuel oil, then you can say it 0.1% m/m.
Sulphur Emission Control Area (SECA)
- It is also called as Emission Control Area (ECA).
- These are the sea areas having stringent regulations for emissions of sulphur oxides.
- MARPOL Annex VI defines the regulations about SECA.
- Today there are 4 Sulphur Emission Control Areas (SECAs): 1. Baltic Sea 2. North Sea 3. North American ECA (USA) 4. US Caribbean ECA.
- SOx emission limits are reduced for these special areas (SECAs).
For attaining the limitations of SECAs, low sulphur fuel is used. For changing the system from low grade fuel to low sulphur fuel, time and correct procedure is required. During entering and exiting from SECAs, all procedures are documented as per MARPOL regulation. Records must contain time, date and location of entry and exit. Quantity of low sulphur fuel and timing of fuel changeover starting and completion are also mentioned in the record.
Control over NOx Emission
NOx emission can be controlled by improving the design of marine diesel engine. Better design of engine can reduce the NOx formation and also there are options for treatment of exhaust gas. Following are some ways to control NOx Emission:
- Miller Principle
- EGR (Exhaust Gas Recirculation)
- SCR (Selective Catalytic Reduction)
- Water Injection (Direct into combustion space & Mixing of water before injection)
- Control over Engine Parameters
- Effective Design of Combustion Space
NOx Emission Limitation
MARPOL Annex VI introduced certain standard for limitation of NOx emissions. A 3-Tier system has introduced for limiting the emissions of NOx. Maximum allowable NOx emission is speed related. As speed increases, formation of NOx decreases exponentially.
Main Engine is a major source of NOx emission and its speed is generally less than 130 rpm and here we’ll discuss about that only.
- It is valid for engines which are installed on ship on or after 1 January 2000 and prior to 1 January 2011.
- It specifies the maximum limit of 17 gm/Kw hour of NOx emission.
- This Tier is no more in use as 2011 has passed.
- It is valid for engines which are installed on ship on or after 1 January 2011.
- It specifies the maximum limit of 14.4 gm/Kw hour of NOx emission.
- At present, this tier is in use globally except special areas.
- It is valid for engines which are installed on ship on or after 1 January 2016.
- It specifies the maximum limit of 3.4 gm/Kw hour of NOx emission.
- It is stipulated for emission control area. It is a drastic change of emission limits from Tier I to Tier III i.e. about 80% reduction of emission.
There are also special areas for NOx emission control like SOx emission control areas. These are called NOx Emission Control Areas (NECAs). At present there are two NECAs: 1. North American Area 2. Caribbean Area
Now it’s important to know that how to ensure that NOx emissions is according to the standard? Wait, there are some stepping stones which help you in this problem.
- EIAPP = Engine International Air Pollution Prevention
- It’s a certificate for marine diesel engine, mandatory for ships according to MARPOL requirements.
- According to requirements of MARPOL, this certificate is issued for engine having power more than 130 KW. This certificate contains the following information: Engine, Model number, Serial number, Power, RPM, Manufacturer etc.
- It is issued when engine is found complying with the NOx emission criteria during the survey before installation of engine on ship. It’s nothing but a certificate for showing that your engine is constructed or following the requirement of NOx emission.
- The supplement to EIAPP is always attached with EIAPP Certificate.
- IAPP = International Air Pollution Prevention Certificate
- According to MARPOL, every ship having gross tonnage 400 and above must carry this certificate.
- This certificate is not only for NOx emission but for all types of air pollutants from ships like SOx, Ozone depleting substances, Incineration, hydrocarbons etc.
- Certificate contains the information about ship particulars, statement regarding compliance with MARPOL Annex VI and date of survey.
Onboard Verification of NOx Emission
EIAPP and AIPP certificates is a proof that engine installed on ship was complying the NOx emissions requirement at the time of installation. But it doesn’t certify that engine is emitting NOx as per the requirements at present. To prove the compliance with NOx emissions, there are 3 famous techniques: 1. Engine Parameter Check technique 2. Simplified Measurement method 3. Direct Measurement method
Engine Parameter Check technique is mostly used by the class surveyors for onboard verification of NOx emission.
NOx Technical File
Now, it’s important to know that which components are checked or inspected during onboard verification of NOx emission. Relax, all these parameters are mentioned in a file, well known as NOx Technical File. It’s a record which contains parameters, details of component and allowable settings which are responsible for NOx emissions.
It is prepared by the manufacturers of engines and approved by respective administration. It is kept onboard throughout the life of vessel. There is one NOx Technical File for each engines for which EIAPP certificates are issued.
Following components of Engine are mentioned in NOx Technical File which can influence the emission:
(Liner, Cylinder head, Piston, Connecting rod, Sealing ring, Fuel pump, Fuel injector, Nozzle, Turbocharger, Camshaft, Charge air cooler)
Note: (No. of Engines = No. of NOx Technical Files = No. of EIAPP Certificates)
NOx Technical Code
MARPOL Annex VI introduced NOx Technical Code in 2008 for controlling the NOx emissions. It includes testing of engine, certification and verification for NOx emissions. NOx Technical File is a part of this code.
At last, I repeat that compliance with SOx and NOx emissions is a directly related to Engines and Fuels. For compliance with SOx emission, use low sulphur fuel as per regulations and for compliance with NOx emission, keep EIAPP Certificates, AIPP Certificate and Maintain components as per NOx Technical Files.