Modern tools ease environmental retrofits and reduce risksAuthor Henrik Bacher
In the autumn of 2014 several more states have ratified the International Ballast Water Management (BWM) Convention. As a result the 35% world fleet tonnage requirement for the convention to enter into force is closer than ever. Once ratified, shipowners that have delayed making BWM preparations and a decision may face a shortage of service and equipment suppliers. Making a timely decision will be key in ensuring compliance. Modern tools such as laser scanning and computational fluid dynamics can be employed to expedite and ease BWM retrofits while also reducing associated risks.
In addition to the impending ratification of the BWM Convention the requirements of the EU sulphur directive also enter into force on 1.1.2015. The sulphur directive sets, among others, requirements for the pH value of wash water from open loop scrubbers.
Laser scanning eases decision making
The space challenge remains a significant issue when considering a retrofit installation of ballast water treatment systems as well as other environmental technology on existing ships. This holds true even if equipment suppliers have been able to develop the technologies to significantly reduce the system footprint.
Numerous environmental technology retrofit cases have shown that laser scanning is an extremely valuable tool in the early design stage of retrofits.
Point clouds generated by laser scanners can be used in combination with powerful 3D modelling tools to compare alternative retrofit solutions (see Picture 1). This significantly facilitates the decision making process. The arrangement for the chosen solution can thus be optimized and at the same time the direct inputs required for making the accurate detail designs needed for prefabrication and installation are created.
Generally the laser scanning required for a ballast water retrofit project takes anything from one to two days and should preferably be conducted while in port. Tankers should always be scanned while in dry dock and spaces should be gas free in order to avoid timely and costly Ex-scanning.
On a BWM retrofit project additional components such as filters and UV reactors commonly have to be integrated with existing ballast water systems. The limited space available means that sharp pipe bends are often needed, which in turn can lead to significant pressure drops and reduced or uneven water flows if not designed correctly.
Carrying out CFD calculations at an early design stage provides designers with a clear indication of the flow elements of the intended arrangement (see Picture 2). This allows them to make the necessary corrections and improvements before any installation takes place.
CFD employed to verify wash water pH values
In order to meet the EU sulphur directive various types of scrubbers are currently being installed on a number of ships operating in Sulphur Emission Control Areas (SECA). The sulphur directive sets requirements, among others, for wash water pH values from open loop scrubbers and how these levels should be verified.
Since verification has proven extremely difficult, if not impossible in practice, significant efforts are currently being made in the European Sustainable Shipping Forum (ESSF) working groups to solve this issue. CFD calculations have been proposed as a reliable and efficient verification solution.
Picture 1. An example of utilizing scanning results from a 106.000 tdw crude/product carrier. The ballast pumps were 1 x 3000 m3/h and 1 x 2500 m3/h. Using point clouds in combination with advanced 3D modelling tools allows different alternative retrofit solutions to be easily compared.
A small investment can lead to significant savings
The costs for both laser scanning and CFD calculations are minor in relation to the overall retrofit investment, but can produce significant savings by reducing risks and eliminating errors.
Many ship owners are currently waiting to the last minute to act. This may lead to a shortage of design and engineering capacity due to the expected bottleneck.
Laser scanning should be carried out in good time in order to create an exact starting point which enables a controlled and systematic design process. Timely and correct implementation of laser scanning can lead to significant long run cost savings.
Picture 2. The CFD calculations show that the BWM solution on the left creates a much more even flow through the four UV reactors than the solution on the right, thus ensuring a more reliable functionality of the installation.
The original text was published in our 2/2014 Top Engineer magazine
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