Exhaust gas scrubbers had been around for a few years, on land more than at sea, before IMO imposed its universal 0.5% sulphur cap on heavy fuel oils (HFO) from 1 January 2020, not forgetting the 0.1% limit on sulphur content in designated emission control areas (ECAs) imposed five years previously.

Alfa Laval, for example, says that its first PureSOx scrubber began operation in 2009. Wärtsilä offers three different scrubber families, to suit various shipboard applications. In addition, Wärtsilä’s lifecycle agreements can include scrubber equipment, such as a recent six-year agreement signed with Malaysia-based Nautica Ship Management, covering two vessels, and ensuring the equipment is maintained at maximum efficiency.

Leading up to the 2020 IMO deadline, scrubbers began to make commercial sense. The IMO rules allowed ships to continue burning high-sulphur HFO if the sulphur oxide gases in the exhaust could be removed so that the smoke stack emissions were reduced to the equivalent of burning 0.5% (or 0.1%) sulphur fuel. The alternative was to switch to lower sulphur fuels, such as distillates (MGO or MDO), which were not only more expensive, but had many other implications such as wear of fuel pumps and systems (the high viscosity and sulphur content associated with HFO offer inherent lubrication properties) and choice of cylinder lubricant (lower alkalinity, i.e. base number, is required for low-sulphur fuels). This latter point proved of particular concern if changing from high- to low-sulphur fuel in ECAs.