There are many critical elements in relation to the design, selection and installation of BWTS. The process is a quadric-modal one which starts with the selection and the design study, followed by detailed study and installation. However, we will confront a lot of challenges in the process. What is critical is what lies below the iceberg. Had the Convention been validated tomorrow, we would need to do 40-50 retrofits every day until the end of 2017. Having that number in mind, it seems that we should not over emphasize the selection process. Unfortunately, we don’t have feedback from BWTS already installed. We are dealing with a case of public pressure putting the regulations ahead of technology. We can apply advanced selection techniques like fuzzy- logic or multi-criteria decision analysis, or simpler statistical grading of questions which can be grouped related to technical, health and safety , financial, operation, installation and maintenance considerations. The one million question is ” are we going to have the time to go through this grading and selection process?”
The installation questions we have is where to place the system, how to integrate it with the remaining machinery and what to do. We have to forget the 3-4 weeks typical approval time from class. This is going to be a much more involved process. Remember that we have to submit not only the usual piping drawings but also structural, electrical and control drawings. We might employ a 3-D laser scanning technique in order to curtail the time needed, instead of the usual survey hand metrics. Utilizing laser cameras which sample at a pace of 1,000,000 points per second, we can have significant time savings, a half-day survey, and we might create point clouds on which we can superimpose the system to be constructed. Of course, the whole process from A to Z can last anywhere from 9 to 18 months, depending on the availability of resources and experience. Other question is what will happen if we do not install a BWTS. The effectiveness of the BWTS is an exponential function of the concentration of the killing agent and the time of exposure. The level of microorganism de-activation achieved, can be increased by applying greater doses of the disinfectant or by increasing the time that the water is in contact with the disinfectant.
It is important that someone knows the limits of the system for example how the effectiveness of the BWTS is affected by temperature and salinity, by the size of installation, how many cubic meters per hour can be treated, space available, if we have to do the treatment during deballasting as well as management of dangerous gases produced during the treatment process and the availability of explosion proof versions. We need to do a hydraulic analysis to determine whether there is a need for boosting. An important element of the system is the filtering which can be mechanical type, screen and disc types or hydraulic. Sometimes filters use the same ballast water to backwash, reducing the flow rate up to 30%. Backwash pumps increase the loss in ballasting capacity.
In filters, we need to avoid the following:
- Clogging
- Mechanical failure
- Restriction in piping
- Corrosion
- Water hammer
- Damage due to foreign particles
- Lack of spares for moving parts
The installation of a BWTS in tankers can be a problem because if the system is not installed in a hazardous area like the pump room, then it becomes the link that connects a safe area with a hazardous area. A golden rule says that everything that is installed in a hazardous area must be explosion proof and and must follow the apparatus and temperature group standards. It is nice and convenient to install the system in the engine room. This can be done, provided that we send the ballast water in the open deck and then from the open deck we penetrate the ballast tanks. Everything that it is installed in a hazardous area, needs to be intrinsically safe and explosion proof. This is not necessary for a system installed in the engine room. For example, one of the solutions is to install the treatment system on deck. But if we install it on deck, we need to take into account the possibility of vacuum creation; therefore we need to install a vacuum breaker valve on the deck piping, preferably downstream the BWTS. The aft peak tank is also a safe area. We can either have a second system servicing the aft peak or the usual recipe, open deck and then through non- return valves go to the ballast tank.
Another solution is, noting that the pump is on a safe area, to connect the aft peak tank with spectacle flange
We can put in the ballast system in the pump room various chemicals, penetrating the E/R bulkhead provided that we follow four safety measures such as reverse flow sensor loop seal, a non return valve and a fail-safe valve.
Another challenge for the BWTS is sampling which must be isokinetic sampling from an area of a well-mixed flow flow. Isokinetic means that the flow velocity in the ballast pipe and the flow velocity in the sampling pipe are equal. Turbulence helps the mixing of the species, so sometimes we enhance it by putting a screen upstream of the sampling pipe. The sampling pipe has a diameter approximately 10% of the ballast pipe diameter.
The problem of time with testing and sampling can be solved with flow cytometry which is a biophysical process of cell counting and sorting. This biomarker is widely used in biochemistry and can be utilized to send automatically data via satellite. By the time the ship comes to port, it may have a certificate of organism-free ballast water. This is a very promising technique, as no time will be lost for sampling and testing.
But what happened to corrosion protection and the need to reduce CO2 footprint? It seems that we have to resort to operational measures such as ballasting at the right place and in the right time. Of course if we can, because ballasting needs to be synchronized with unloading and vice versa.
Unfortunately, very few operators like to be pioneers when it comes to buying new equipment. They prefer to learn from the mistakes of other rather than make mistakes themselves. It is a fact of life that everybody wants to be on the high side of the boat. All of us working in the shipping industry, should bear in mind that we are riding the same boat..
Above article is an edited version of John Kokarakis presentation during 2014 GREEN4SEA Forum
More details may be found by viewing his Presentation video
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.
