With the almost complete phase out of Tier II new-building slots on our door step, along with the plethora of emissions related articles seemingly published every other day, this week we will take a look at the pros and cons of different fuels, their emissions/by products, and conclude with possibly one of the best interim alternatives to the present emissions problem said Allied Shipbroking in its latest weekly report.

According to Gerry Lathrop, Research Analyst of Allied Shipbroking, Fuel oil(s) probably account for the largest percentage of marine fuels by weight consumed. The reason for this is quite simple, it’s incredibly cheap while they are also quite energy dense (around .97 – 1.0 sg or tons per cubic meter) when compared to other alternatives such as diesel (.85 sg) methanol (0.79 sg), LPG of equal parts C3 and C4 atoms (0.537 sg) and LNG (0.45 sg). In general, fuel oil releases the most carbon dioxide (CO2) during combustion, about 3.11 tons of CO2 per ton of product, followed by LPG at 3.01 mts, LNG 2.75mts, diesel 2.63 mts and methanol at 1.37 mts. Many of you may be thinking, how can 1 ton of product create 2 tons of CO2? The answer lies in the chemistry of the combustion process. Simply put, combustion takes carbon from the fuel, and adds oxygen from the atmosphere and releases energy. The oxygen in this case makes up more than 2 thirds of the CO2 molecules.

But where do NOx and SOx fall into play? Unfortunately, NOx and SOx emissions are not as straight forward to quantify. For example, Gerry Lathrop, Research Analyst of Allied Shipbroking further noted, the total sulfur content of a given fuel is heavily dependent on where it was sourced, while removing sulfur is quite difficult and expensive. For that reason, giving any concrete figures for fuel oil and diesel can be inaccurate. On the other hand, LNG and LPG often have their sulfur content removed through the use of an acid gas removal unit (AGR), which is then processed in a sulfur recovery unit (SRU). Unfortunately, NOx emissions are similar to SOx emissions in that they are not fixed. However, NOx differs from SOx, as the same fuel may produce little NOx emissions in one engine, and higher emissions in another. Similarly, the same engine may produce no NOx emissions at one speed or engine load, and then at full speed, may produce a significant amount of the pollutant. The main source of NOx in fuels stems from the high heat reached during combustion. In order to produce little NOx, the temperature inside and around the engine must be lower than about 760 degrees Celsius. Methanol, LNG, and LPG burn at lower temperatures than other fuels, and thus could produce lower amounts of NOx emissions. How does all this fit into the industries search for lowering harmful emissions? Well as there is yet to emerge a single fuel that is clean and has negligible harmful emissions, the cheapest and probably best alternative right now seems to be the scrubber. Scrubbers work by physically and chemically cleaning the harmful emissions inside the exhaust. This is done by spraying water over the gas in the smokestack and then either discharging it into the ocean in the case of open loop systems, or cleaning the water through the use of chemicals or filters, and then reusing the water again in the case of closed loop scrubbers. This is possibly a better interim solution for commercial shipping emissions, as LNG powered vessels can be more costly to buy and maintain, while retrofitting a vessel to run on LNG will probably cost more than a scrubber in most cases, especially when taking into consideration the technical and space restricting challenges that are usually involved in the case of switching to LNG.