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Selecting the most suitable ballast water treatment system

The International Maritime Organization’s International Convention for the Control and Management of Ships' Ballast Water and Sediments (BWM) will enter into force on 8 September 2017. Thereafter ship owners will need to fulfil the convention and in practice install a ballast water treatment system (BWTS) on their ships in accordance with the schedule related to the renewal of the IOPP certificate. There may be a difficult road ahead before installation as the selection of the system is far from a simple procedure. Once the system is selected, this is followed by design, installation and commissioning. Several stakeholders are involved: the shipowner, BWTS-vendor, classification society, shipyard, contractors, design companies, and consultants.

Ballast Water Management Treatment Guide

Retrofit project 

According to the BWM convention, ship owners must in practice install a ballast water treatment system (BWTS) on their ships. Alternative solutions are in most cases not an option. A BWTS installation project, or a BWTS retrofit, includes various phases i.e. evaluating solutions and the selection of suitable system, design, installation, including prefabrication and commissioning. Design includes system integration design and installation or detail design. Between the two design phases there is normally the classification society approval. 

Estimations for BWTS retrofit projects vary, but it should take around nine months, if the process is carried out in a systematic manner that aims for the most suitable solution, which is always ship-specific. After the convention enters into force there may be many bottlenecks due to the vast increase in demand. Lack of capacity for stakeholders classification societies, BWTS vendors, installation, docking, and design can all delay the retrofit process.

The result of the feasibility study, the first phase of a BWTS retrofit, provides a shortlist for the best alternatives for each vessel. The selection for the shortlist is based on several technical and economic criteria.  Different systems, methods and vendors are compared. Also the operational costs, the footprint of the required equipment and operational aspects such as water quality, total ballast volume and ballasting cycles per year are considered. At this point investment costs are compered as well.  3D scanning is performed and 3D models of different systems are modelled into a point cloud, which is produced via 3D scanning. Preliminary cable routes are done in the 3D model as well. BWTS usually require space for maintenance and repairs. Sufficient space reservations for maintenance can be verified with 3D design.

The final selection is made from the shortlisted alternatives according to normal commercial negotiations and decisions

Design starts with updating the relevant system diagrams. Possible clashes with other systems or pipes need to be identified as early as possible, therefore accurate design methods are preferred. Laser scanning is a proven tool for creating an accurate starting point for design which is preferably done in 3D. The later clashes are identified, the greater is the impact on the schedule and costs. Another important issue is the hauling plan. The system components are large, and hauling may not be possible via normal routes. 

After system diagrams and other drawings are sent for class approval, the design regarding installation and pre-fabrication is started. Detail design has a significant effect on the successful installation and completion of the retrofit project. The better and more careful the design, the less time is spent at the yard or in the dry-dock, where the installation is normally done. Optimal design is essential for minimum off-hire and the successful and timely completion of the installation. 

Variety of treatment methods and vendors

Treatment methods can be divided into physical and chemical methods. Filtration, UV-radiation, cavitation, pressure vacuum and heat, among others, are physical methods. Chemical methods include (but are not limited to) chlorination, electro chlorination and ozonation. Each method has its pros and cons. 

The footprint, operational costs and need for spare parts and maintenance will differ between different methods. The methods can be seen as compromises; the goal is not to find absolutely best solution, but a solution that best fits the current situation. 

The backgrounds of vendors vary as well. Some vendors have a background in water treatment for land-based applications, some are in the marine business with a variety of products and some vendors have only one product, a ballast water treatment system (BWTS). 

The main concern for the ship owner is to find a BWTS that fulfils the rules of the IMO and flag authorities as well as ship-specific requirements including the water characteristics where it is operated. The selected system should also be cost efficient and the operating the system should not cause problems for the ship’s existing systems or require extra efforts from the ship’s crew.

Criteria for selecting the best solution

Each ship can be compared to fingerprints; even if they look alike, there are several differences that make each ship and fingerprint unique. The ship’s size, age, type, ballast water capacity and ballast pump(s) capacity, and ballasting frequency are issues to consider when choosing the best alternative. The ship’s route, including water characteristics and the length of voyage, also have an influence. 

The ship’s remaining lifetime and annual ballast volume define the overall costs of the installed BWTS. The operational costs of the BWTS consist of the cost of consumables (electricity, chemicals) and spare parts. 

Machinery spaces on ships are normally used efficiently, which means that there is minimal extra space, if any, available. It is likely that the BWTS is installed in machinery spaces such as engine rooms. The electrical capacity may be limited and there is no surplus for all types of BWTS. Therefore, updating the electric balance calculations is essential to ensure compliance of the selected BWTS. 

Another concern is the pressure drop as a result of the increased pipe meters and components. That might lead to a need to modify or even replace ballast pumps to keep the ballasting capacity as initially required.

Some vendors set numeral limits for water characteristics such as salinity or Ultraviolet Violet Transmittance. The responsibility for fulfilling the IMO convention is the ship owner’s, even if the system itself has type approval. Therefore, it is very important to verify the operability of the BWTS before acquisition. Computational Fluid Dynamics (CFD) is a method that can be used to verify the desired operability (pressure drop, fluid distribution) of the ballast water system after BWTS installation.

There are many solutions and different kinds of circumstances. Therefore, the best alternative for a particular vessel may not be applicable to another. 

The ship may have a BWTS that works well while sailing in salty ocean water, but might face problems while moving to fresh waters. A similar situation could occur if a ship that is used in legs that take several days, is moved to shorter legs that take only hours. These examples may concern some ship owners and can even affect a ship’s second hand value or at least its operability in certain areas. A similar problem can be differences in legislation between the IMO and the United States Coast Guard (USCG): it could happen that a BWTS has IMO type approval, but not USCG’s. Without USCG approval the ship cannot be operated in US waters. 

Future challenges

The demand for BWTS is set to rise drastically leading up to September 2017. There are tens of thousands of ships in the world that require BWTS installations. This can lead to longer delivery times. Besides the availability of BWTS, the capacity of design companies and docking may also be limited. The high demand will likely lead to higher prices for both equipment and services. A lot of investments have been made into developing equipment and systems and payback is expected. It is also possible that some systems may be more popular than others, which will certainly affect the prices of the systems. The sooner the retrofit project starts the more desired is the outcome, both timewise and from a cost perspective. It is essential for ship owners to act now to avoid the above-mentioned difficulties. 

Authors: Henrik Bachér and Olli Leino

Selecting the most suitable ballast water treatment system
There are many solutions and different kinds of circumstances. Therefore, the best alternative for a particular vessel may not be applicable to another.

Figure 2. An example of Computational Fluid Dynamics (CFD) visualization. CFD can be used to analyze the stream velocities in BWTS.

Figure 1. The outcome of a feasibility study could look like this. The grayscale parts are the outcome of laser scanning, the coloured objects are part of the BWTS. The desired design result and a cost-effective and feasible retrofit project with successful installation can be achieved with accurate design tools and the right expertise.

Figure 2. An example of Computational Fluid Dynamics (CFD) visualization. CFD can be used to analyze the stream velocities in BWTS.