Below are some of the latest technologies and methods that are employed on board in order for a ship to comply with the standard set for reducing pollution in the marine environment.
NOx is emitted in the ship engine’s exhaust when the nitrogen in the air reacts with the high combustion temperature. Here are the methods used in order to reduce ships Nox emission.
- EGR or Exhaust Gas Recirculation. This method is done by sending back some of the gases from the engines exhaust to the scavenge space. There the gases mix with air which will later be used as supply for the cylinder combustion. This way, the oxygen in the air is reduced thereby resulting in NOx reduction.
- Humid Air. The water vapour in this method is mixed with the combustion air. The mixture is then supplied to the cylinder. Using this method can help achieve NOx reduction by around 70-80%.
- Water Injection and Emulsion. This method utilizes water as an additive in order to lower the combustion temperature which results in a lower NOx emission. In the case of water emulsion, water is mixed with fuel while in water injection, there is an injector placed in the cylinder which injects fresh water. The downside of this method is that the combustion of specific fuel oil is increased and the NOx emission is only reduced by 20-45%.
- SCR or Selective Catalytic Reduction. This method is found to be the most effective among other when it comes to reducing NOx emissions in ships. The percentage of reduction is estimated to be 90-95%. Low sulphur fuel oil is used in this method while the temperature of the exhaust is maintained at 300 degrees Celsius or above. The only drawback of selective catalytic reduction is the cost of operation and the expansive installation.
- Two-Stage Turbocharger. The latest innovation of the two-stage turbochanger can help lower the temperature of the exhaust in the intecoolers and it can also help achieve lowering the NOx content in the emission of the exhaust.
- High Compression Ratio and Scavenge Pressure. With this method, introduction of large amount of air into the cylinder is possible. The temperature of the lower combustion is then lowered as well as the NOx emission.