Conditioning the sea water for evaporators - fresh water generators of Queen Mary 2 and Queen Elisabeth 2

The Queen Elisabeth 2 and the Queen Mary 2 both are owned by Cunard Lines ,England and are known as first class luxury cruise liners. Queen Elisabeth 2 is now used as a hotel ship in Dubai. Queen Mary 2 is during the summer regularly crossing the Atlantic from Southampton to New York and during winter cruising in the southern hemisphere. There is a lot of drinking water needed on these ships. For instance the Queen Mary 2 has a capacity of 2600 passengers and a crew of another 1500 people; in addition there are 3 swimming pools on board. This water has to be produced on sea, because it would be impossible to carry enough water for all the people to cross the Atlantic in 6 days. There are a row of so called evaporators installed, in the case of the Queen Mary 2 there are six of them, each of these with a capacity of 3000 litre an hour.

The common problem on such systems, the capacity of these evaporators has during the production of drinking water slowly declined. The reason the scale mainly formed out of NaCl the salt in the Seawater, as well as CaCO3 known as lime scale, which is also found in seawater.
Scales on the inner surfaces reduce the heat transfer, as a result less water can be evaporated, the efficiency drops and the production gets less.

Once the capacity has declined to a certain limit, the evaporator has to be manually cleaned. Even if there has been chemicals added to avoid the scaling in the evaporators, but they slowed down the scaling at the best. So every few weeks the evaporator has to be shut down opened and cleaned by the use of chemicals and manually with brushes.
At the common sea water inlet as well in front of each evaporator a Merus ring was installed. After the installation of the Merus Rings the production capacity of the evaporators was closely checked and compared to the historical data. It could be seen the capacity of each evaporator stays stable.

So customer decided to open and see evaporator and check the results visually. After seeing the results, and verifying the over several months the stability of these, the customer decided to stop adding of scale inhibitors. Since the installation at Queen Elisabeth 2 in 2004 and at Queen Mary 2 in 2006  no cleaning required anymore, and the production of each of the evaporator is stable. The ROI (return of Investment) was in accordance to the customer in both cases less than 4 month.