Emissions from ships and barges : VOC and odour removal

• Sources of emissions.

Emissions are likely to be released in dock during the loading and unloading of ships’ tanks.

Vapours may also be released during the cleaning of ships and barges while in dock.

Another source is degassing: the opening of the hold to release vapours. Vessels are often degassed during their journeys but when this occurs on inland waterways, it can lead to complaints from communities nearby. The CDNI is progressively banning degassing unless the ship is in dock, where emissions can be treated.

• Pollutants

Pollutants commonly emitted include hydrocarbons such as naphtha or benzene. These can be harmful to human health and the environment, and are subject to strict emissions limits.

Many emissions contain odorous chemicals, e.g. crude oil can produce a sulphurous smell. The local environmental authorities can take action against companies which cause an odour nuisance.

• Flow rates and concentrations

For smaller barges, around 2-3 000 m³ in size, the flowrate during the loading and unloading process is typically relatively low: around 200-600 m³/h. The process usually lasts for five-six hours.

Larger ships might have flow rates of 1 500 m³/h, and the process can take up to 24 hours.

The concentration of pollutants depends on several factors, including volatility of the transported product and temperature. It ranges from several hundred milligrams to several grams of VOCs per m³, but tends to be towards the higher end of this range.

• Treatment technology: incineration

Mobile vapour combustion systems are commonly installed at docks.

They incinerate gases, destroying the contaminants but resulting in CO₂ emissions which enhance climate change. Therefore, this is not always an environmentally friendly solution in the long term.

Installation of incineration units is expensive and complex, and they require an operator on site whenever they are in use.

Incineration is best suited to treat very volatile compounds, such as ethanol or naphtha; or for situations where treatment is required 24/7, such as at busy tank terminals. In these cases, activated carbon might be unsuitable as the consumption of carbon could be too high.

• Treatment technology: activated carbon filtration

Activated carbon filtration is also widely used to treat emissions from ships and barges.

The carbon is consumed only when contaminants are present, making this a more suitable technology than incineration in situations where treatment is discontinuous or concentrations of contaminants are low.

Activated carbon is also a greener solution than incineration: it does not produce CO₂ emissions, and waste carbon can be reactivated.

While the filters are in use, no operator is required on site.

This client loads specialty chemicals onto barges. The chemicals are chlorinated solvents, which are potentially harmful to the environment and human health. For the specific molecule in this case, they are subject to an emission limit of 1 mg/m³.

The maximum flow rate during the process is 600 m³/h, and loading takes 5-8 hours.

The company already had a scrubber and incinerator on site to treat other compounds. However, these chlorinated solvents are corrosive, and would damage this technology.

DESOTEC supplied an AIRCON 2000 filter in 2015, which has been working well ever since.