Desulfurization of Heavy Fuel Oil Processing - Energy and Emissions
Hydrogen-rich recycled gas is injected to the HFO before it is pumped through a heat exchanger. From here it is fed through a fired heater where it is heated to 300-400°C @ between 30 and 130 bar, causing it to become vaporized.
This vapor now passes through a fixed bed reactor where in the presence of a catalyst, a hydro-desulfurization reaction occurs.
The resultant gas is then cooled to 35°C and 5 bar before being passed through the stripper tower where any remaining H2S is removed. The liquid gathering at the bottom of the stripper is the desulfurized heavy fuel oil. One method of achieving this is shown below.
Now, this process is quite efficient but energy intensive due to the high temperatures and pressures required in circulating and vaporizing the HFO. This is accompanied by the emissions of gasses to the atmosphere that consist largely CO2, one of the most prominent of the greenhouse gasses.
So, we have to weigh up the damage caused by these gasses produced in the desulfurization process against the benefit of the reduction in sulfur dioxide and decide if the process is worth while.
According to some of the leading scientists who are experts on these matters, the CO2 produced will increase total anthropogenic emissions by 0.01%, but make savings of overall SOx emissions from combustion of the desulfurized HFO by ship's engines of 6%.
As a marine engineer I tend to support the desulfurization of the HFO, not only because of the reduction in SOx emissions to the atmosphere, but the added benefit to the ships engines running on low-sulfur fuel.
I have seen the damage to pistons, liners, fuel injectors and pumps through sulfuric acid attack, as well as the problems caused by acid entering the lube oil system. The penalty to the ship owners is of course the cost of the reformulated fuel. However, this must be compared with the savings on engine parts/maintenance, and lube-oil changes, before deciding to use the low-sulfur fuel or, to fit gas scrubbers to mitigate the SOx in their ships exhaust system.
maritimejournal: Facts on ships exhaust emissions.
dnv: IMO and MARPOL Emission data.
ritmdl: Reformulated HFO-emissions compared.
ec.europa: SO2 content in HFO
sciencedaily: reformulated fuel processing emissions causing concern.