Scrubbers are one of the available solutions for compliance with IMO 2020 regulation which offers the possibility to keep using HFO for the vessels and avoid potential problems with low Sulphur fuels for which not much information exists. While a big boom for scrubbers was noticed especially in 2018 until mid-2019, the demand now is a little bit down due to the price difference between LSFO and HSFO.

As long as price is very low, it is clear that the investment does not make sense; not so many will go for scrubbers. But what we expect, and also many others are expecting it, this will change in certain time, because also the production of LSFO causes money and so there is logic that there is a price difference.

Currently, we have 3,900 scrubbers in operation; most of them are open-loop and a certain amount is left; about 20,000 vessels can use scrubbers in the future. If you see where scrubbers are used, many of them are used for bulk carriers, container ships or tankers. We also see that this will change much in the future.

Regarding scrubber technologies; inline scrubbers have the possibility to run into trial mode. U type scrubbers can be operated in hybrid mode or open loop. Open loop is a very simple process: You take the seawater, you wash the Sulphur dioxide and you give it back to the sea. The Sulphur dioxide reacts with the alkaline compound of the seawater, which are sodium hydro carbonates, calcium hydro carbonates. These react to sulphur and this is released to the sea.

A lot of discussion is around on how dangerous is this discharge of the water back to the sea. I would say seawater has a concentration of around 2,700 mg sulphate per litre so whatever you add is sulphate from the scrubber which must not be taken into account; it is minimum amount.

When you go to closed loop operation, you can use different alkaline solutions like sodium hydroxide, magnesium hydroxide to operate and, in this case, you have a zero discharge.

There are also a lot of different technologies available: Specially for the U type scrubbers, there are packed towers. Like an open spray tower, a packed tower is a tower when you feel in packings. These can be melting of polyethylene packings, random packings.

However, there are some disadvantages with these packings. We decided not to go for packed scrubbers but to use the open spray scrubbers which have no internals and to optimize this scrubber sounded comparable to packed towers.

What are the advantages of open sprayers? You have an increased overall safety, you will not see any problem with meltings of packing or even with spill ups of packing, contaminations etc.

You also have reduced pressure drop and the most important advantage is the footprint, when it goes to open sprayder, it can operate in higher velocities, so it can make the scrubber around 20% smaller than a packed tower and, what we learned is, that space is always a topic of constraints onboard vessels. Finally, also the weight is reduced.

So how do we optimize our spreaders? We can optimize distribution of the vessel inside the scrubbers, we can install some devices which guide the flow gas through the scrubber. Overall, the target is to maximize the uniformity of the flow gas. The gas goes through the scrubber and, whenever you do not have uniform gas flow, it means the scrubber is not operating in the right way. You have pipe streams which increases the SO2 going out and increases the SO2 removal efficiency.

We invested last year a lot of time and development for defining User Defined Functions (UDFs), to simulate what is the droplet doing when it hits the wall, how the CO2 is removed and what happens when a droplet hits another droplet.

A recycle of such simulation: After changing some the spray banks and installing some guiding devices, we found quite a uniform flow distribution. What is the target of such a simulation? In a scrubber simulation, the scrubber must be optimized, because you have to consider the scrubber must work at an 85% engine load but also a 25% engine load. What also the CFD does is to simulate the discharge water mixing. According to IMO regulation, we have to reach more than 6.5 pH for 4.5 meters distance from the discharge point.

Our lessons learned so far from the project we have executed are:

The first point is material selection. I think material selection must be influenced or specified by the maker, as we have the knowledge what remains in the flow gas after scrubber. You have low temperatures but cost by the low temperatures, you have some concentration of sulphur acid, which is really aggressive, so you must not go to low grade materials, you must use higher-grade steel materials. So you cannot delegate this responsibility to the owner or even to the shipyard. This is our experience. Otherwise, you have problems, like corrosion.

Corrosion is also a major topic during installation. Installation at the shipyard requires supervision from the maker because not all the shipyards are taking care of the high grade materials and so very often there is choice of material not covering the scrubber made of SMO and then you have severe corrosion.

Another topic, also known from many other projects, is the measuring of instruments. Measurement devices have a higher tendency to make problems, so it is necessary to choose the right equipment and also have the spare parts available.

Above text is an edited version of Mr. Bärnthaler’s presentation during the 2020 GREEN4SEA Athens Forum.

You may watch his presentation herebelow

The views expressed in this article are solely those of the author and do not necessarily represent those of SAFETY4SEA and are for information sharing and discussion purposes only.


Klaus Bärnthaler, Vice President – Marine Solutions, ANDRITZ AG

Dr. Klaus Baernthaler is currently Vice President for Maritime solutions in the Air Pollution Control Division of ANDRITZ AG. For the maritime market, ANDRITZ provides all types of scrubber solution for SOx removal as well as a Dry Exhaust Gas Cleaning System for multipollutant control.

He is holding a PHD degree in Chemical Engineering from the technical university in Graz / Austria. In 1992 he started his professional life as process engineer for flue gas cleaning at Austrian Energy & Environment (AE&E). During his work for AE&E he was promoted to Head of  Engineering Department and in 2007 he took over the responsibility of Business Unit Manager for the total Air Pollution Control business of AE&E. During this time many large and Turn Key Exhaust Gas Cleaning plants were installed by AE&E and later ANDRITZ worldwide on land. In 2011 Klaus joint ANDRITZ with the same responsible role and took over the responsibility to build up the maritime business in 2018.