More effective exhaust gas cleaning thanks to scrubber with upstream soot separator: SO_x and fine dust content is reduced by up to 97 percent

More stringent IMO regulations from 2015

To reduce sulfur dioxide emissions on a long-term basis, the sulfur content in the exhaust gases of ships should be reduced from 3.5 percent at present to 0.5 percent by the year 2020 according to the International Maritime Organization (IMO). As of 2015, there will even be a limit of 0.1 percent in the North Sea and Baltic Sea, for example – a problem for many tankers, freighters and other types of vessels that operate in this region. To comply many will  have to be converted to other fuels at great expense. A less expensive, but just as effective alternative is retrofitting with scrubbers (exhaust gas cleaning devices). To further improve the effectiveness of the scrubbing process SAACKE GmbH now uses a special solids separator in its systems in which a major portion of the soot is separated before desulfurization. This makes it possible to filter out up to 97 percent of the fine dust and sulfur dioxide, thus reducing air pollution to a minimum.

Currently there are around 50,000 vessels sailing the seven seas that altogether consume about 370 million tons of heavy fuel oil a year. Highly toxic components of the exhaust gas like sulfur dioxide, which is produced during the combustion of heavy fuel oil, were simply emitted into the environment for decades. Among other things, such oxidation products are a cause of the much feared acid rain, which contaminates the ecosystems of the world. For this reason the IMO has tightened its regulations in recent years. In the North and Baltic Seas, for instance, there are already SO_x emission control areas (SECA), in which a sulfur limit of one percent applies. As of 2015, this will drop further to 0.1 percent. This limit has already applied to all European ports since 2010.

Shipping companies have already responded to the new and coming regulations. When new ships are built, therefore, the owners either attempt to do without heavy fuel oil or to equip them with scrubbers. However, for all vessels currently in operation on the seven seas it would be expensive and, in some cases, even impossible to convert them to other fuels. In this case it would be economically more efficient to retrofit them with a scrubber since the purchase costs are amortized after only two years in many cases. As a rule, these devices operate with spray nozzles in which the exhaust gases are brought into contact with a fine water mist. In closed systems the washing water is mixed with sodium hydroxide to dissolve the sulfur out of the exhaust gas. However, this requires a considerable amount of water in which the chemical agent additionally has to be dissolved.

To implement more compact systems and avoid having to carry additives on board, seawater is usually used in scrubbers. The alkalis contained in seawater bind the sulfur without the necessity of chemical additives. In this process seawater is pumped into the scrubber and utilized in the spray nozzle. In the first cleaning stage the exhaust gases are fed through a kind of spray mist, in the second stage they go through a water cascade. The contaminated seawater can then be diluted with pure seawater in an open loop until the pH value reaches a normal level again and – in accordance with the IMO provisions – discharged into the sea. Another option is to mix the contaminated water with lime in a closed loop. The resulting mixture can subsequently be used again.

To further improve the cleaning capacity of the scrubber and thus be prepared for future requirements, SAACKE additionally employs a special fan (VentSep) with an integrated separator. In this way the solids are removed from the exhaust gas even before nozzle scrubbing. The separated particles thus no longer enter the seawater, making disposal easier. Since the VentSep reliably separates all particles from a size of 2-3 µm, it is possible to filter out and collect a substantial portion of the soot. During nozzle scrubbing the soot would otherwise form a sludgy mass that is difficult to dispose of. The previously separated soot, by contrast, can be stored on the ship and then later be taken ashore.
At exhaust gas temperatures in the normal range the VentSep can be placed directly in the exhaust gas flow of a boiler. Should the temperatures exceed a certain limit, however, it is necessary to connect a heat exchanger in between. In addition to boilers, the scrubber can also be connected to the driving engine. The advantage here is that connected flue gas heat exchangers are no longer contaminated. This reduces cleaning and maintenance requirements significantly.