Maritime flue gas cleaning

Environmental protection for seagoing vessels

Expensive fuels versus contemporary exhaust air purification

Strict limits for SOx and NOx

In recent years, the International Maritime Organization (IMO) has continuously and significantly reduced emission limits for sulfur oxides (SOx) and nitrogen oxides (NOx) from ship exhaust.

MARPOL Annex VI Regulation 14 sets limits for the sulfur content in fuels and distinguishes between two zones: A sulfur content of 0.1 % is permitted for emission control areas (ECAs) in coastal waters; outside these zones, a maximum of 0.5% sulfur is permitted in the fuel.

MARPOL Annex VI Regulation 4 allows the use of exhaust gas cleaning systems as an alternative method to comply with Regulation 14 - with corresponding limits for SOx, measured as SO2, according to the following table.

The NOx emission limits were set in MARPOL Annex VI Regulation 13:

In addition, according to the IMO, fuel consumption data must be collected and documented for all ships of 5,000 gross tons or more as of January 1, 2019. This affects more than 34,000 ships worldwide.

In the future, a blueprint known as IMO 2030 also aims to reduce carbon dioxide emissions from global shipping by 40 percent by 2030 and 70 percent by 2050 compared to 2008 levels.

Alternative fuels are not a short- or medium-term alternative

The switch to low sulfur diesel, LNG or LPG could help reduce some of the emissions. However, the problem of nitrogen oxide emission and the generation of soot and ash from the combustion process remains.

Energy Watch scientists also conclude that any CO2 savings are far outweighed by the high methane emissions from natural gas, so a switch from petroleum to natural gas in the transportation sector actually significantly outweighs the negative climate impact of petroleum. Whether low-sulfur diesel, LNG, or LPG, there are significantly higher costs for the fuel as well as inevitable conversion costs for the existing engines - compared to the continued use of relatively inexpensive heavy fuel diesel in combination with a contemporary exhaust gas cleaning system.

The existing price difference between low-sulfur light oil and conventional heavy oil has remained significant for years and usually leads to an ROI of well below three years for retrofitting modern exhaust gas treatment.

Classic flue gas treatment must be adapted to maritime application

The flue gas scrubbing processes used to date, designed as pure wet scrubbers or scrubbers, produce wastewater and waste materials. The waste water that is discharged also contains salts which cause additional damage to the environment. In addition, these processes produce an intensive white waste gas plume - caused by the harmful sulfuric acid aerosols formed in the process, as these are only partially removed from the flue gas using scrubbers.

Waste-water- and waste-free flue gas scrubbing for seagoing vessels

To eliminate the problems described above, Steuler Equipment Engineering has developed a modular flue gas treatment process in which

  • no waste water and waste materials are produced,
  • there is no visible vapor plume,
  • the required emissions are reliably met,
  • installation and operation on seagoing vessels are possible.

This dry flue gas scrubbing with sodium hydrogen carbonate, i.e. baking soda, has proven itself hundreds of times on land, i.e. in flue gas treatment plants downstream of heavy oil engines.

And it does so at low operating costs, so that the process pays for itself in the short term compared with a switch to more environmentally friendly fuels. The system developed by Steuler uses chemical/physical processes to remove the pollutants from the exhaust gas stream and converts them into water, nitrogen, sodium sulfite as well as sodium sulfate in several stages. In addition, the soot and ash particles are also separated.

With partners, we not only enable the supply of operating materials (baking powder and urea) in the port, but at the same time the return of the residual materials. These residual materials do not have to be landfilled, but can either be used in concrete production through re-salting or serve as mine backfill to fill underground cavities. This prevents subsidence at the earth‘s surface, which would occur during the mining of sedimentary mineral resources (e.g. coal, ores, salts).

The engineers at Steuler Equipment Engineering have succeeded in designing such a plant - the basic principle of which has proven itself for many years in large plants on land - in such a compact form that it can be integrated into seagoing vessels. All modules can be installed and operated together or as individual modules. The system is free of waste water and waste and is significantly more economical than the alternatives.

Denitrification as an option

The emissions of NOx are in many cases still below the emission limits according to "MARPOL Annex VI Regulation 13", so that denitrification using SCR catalysts is not always necessary. However, a joint assessment with the ship owner based on the specific operating profile of the ship can be made very quickly.

This area of flue gas cleaning is also one of the core competencies of Steuler Equipment Engineering, which has been mastered for decades, with thousands of completed projects in this specific loading case.

Installation of the necessary catalysts is possible in containers above the engine room and can thus be easily maintained at the same time.

Request a quote at short notice

Depending on the application, the ROI ist between 1 and 3 years!

The following information is necessary for an initial design and calculation:

  • Engine power
  • Fuel consumption
  • Flue gas temperature at the engine/turbocharger outlet
  • Sulfur content in fuel or marine fuel (e.g. IFO 380)
  • Speed (for determining the emission values for NOx)
  • Operating profile (days at sea, days in port, stockpiling time of a bunkering operation)
  • Type of ship or space conditions in the engine room or adjacent areas