With the entry into force of the IMO Ballast Water Convention in September 2017, shipowners have been calling on a Finnish shipbuilding and offshore engineering company to conduct an independent evaluation of its ballast water management system modification plan
The addition of signatures to the 2004 International Convention for the Control and Management of Ships’ Ballast Water and Sediments in recent months does not conceal the fact that this is an IMO measure that has been resisted since it was conceived. The 52 countries that have signed on the IMO now exceed the required 30, but “only” account for 35.1441% of the world’s tonnage, which is just over the 35% threshold required for ratification to take effect 12 months later. Now, the legal “instrument” seems imminent, but it has not yet been completed.
However, in 2016, shipowners took matters into their own hands and firmly believed that there was an urgent need to provide technical answers to the best ballast water management system performance for existing ships.
Foreship, a leading shipbuilding and offshore engineering consulting company, has recently been providing detailed recommendations on retrofit options, and the feasibility study covers a single ship. Foreship is evaluating different technical solutions and similar technologies for various ship types and ship ages from different suppliers, and evaluating the overall installation work, installation location, and temporary and permanent structural modifications.
Olli Somerkallio, head of Foreship’s machinery department, explained that although the choice between systems will definitely be guided by cost, the comparison may not be that simple.
“We focused on the technical aspects of the installation, namely equipment space, plumbing and electrical compatibility,” Somerkallio said. “To produce meaningful results, expertise in shipbuilding, ocean engineering and ship behavior is required.”
The cruise ship industry’s ballast water flow rate requirements are usually less than 500 cubic meters per hour, which has prompted ship owners to choose ultraviolet-based BWMS technology, which makes invasive species “unsurvivable” rather than killing them. However, as widely reported, the U.S. Coast Guard has not yet finally approved the UV test standard.
In addition, UV devices are impractical for the large flow rates required by the main ballast water system on large cargo ships (such as oil tankers and bulk carriers). Here, electrochlorination (EC) has become the preferred solution. EC produces chlorine-based disinfectants by passing a direct current through water to react with sodium chloride. The resulting free chlorine will kill bacteria and other microorganisms in the ballast tanks. In the de-ballasting stage, the chlorine content is measured and neutralizing agent is introduced as needed.
Somerkallio suggested that shipowners should be aware that the additional pipes, related fittings and valves required by the ballast water management system, as well as the ballast water management system itself, are all sources of pressure loss, and which ballast pumps must have sufficient head pressure to solve them. He said that Foreship uses pressure loss analysis as part of its feasibility study because sometimes it is necessary to upgrade the pump impeller or motor. “In the worst case, the entire pump may need to be replaced,” he said.
Somerkallio said that special consideration must also be given to tankers, because ballast water operations take place at the bow and stern, and the stern ballast tanks usually contain more than three-quarters of water-which is essential for the unimpeded operation of the ship. Here, the main ballast system pump is located in the cargo pump room (hazardous area), so it cannot be used to pump water to the tip tank located in the safe area. The rear pump cannot be directly connected to the main BWMS.
A typical medium-range oil tanker may have a flow requirement of 2000 m3/h for the main ballast system, which is divided into port and starboard ballast tanks. This can be handled by two BWMSs each with a capacity of 1000m3/h or a single BWMS, where both pumps are connected to the same treatment system. The individual aft tank ballast water demand will be handled by a universal service pump, connected to a smaller BWMS, with a flow rate of 250-300 cubic meters per hour (for example).
A recent Foreship feasibility study evaluated in detail two EC solutions from competing manufacturers: one adopts EC in the mainstream; on the other hand, EC occurs in a tributary, and “chemicals” are introduced into ballast tanks.
Somerkallio says that, in fact, mainstream systems are less complex, lighter, and smaller, and consume about 25% less power than sidestream systems. However, he added that attributes related to installation, performance, and safety can convince a sidestream solution.
“For example, according to a manufacturer, due to the special electrode design and materials, its mainstream EC system can operate at extremely low salinity, but it is impossible to operate in almost zero salinity waters such as the Great Lakes. Side The flow system does not have such restrictions; if the salinity is below 15 PSU, the stored seawater can be used.”
Lateral flow systems can also operate in colder water better than mainstream systems.
Similarly, the volume of the sidestream system may be twice that of the mainstream system, and the weight has increased by 60%. This is an unavoidable fact, but Somerkallio pointed out that it is more important to ask where the additional BWMS takes up space. He explained that the mainstream system forward requires a larger additional deckhouse for two EC units and two filters, while a smaller lateral flow deckhouse solution brings greater benefits to the EC unit and other auxiliary equipment. Positioning degrees of freedom.
In terms of floor space, mainstream solutions may require two-thirds of the area required for side flow solutions, but if a single side flow system works across two pumps, the difference is almost negligible.
Similarly, the EC process separation required by the side-stream system requires twice the number of pipes as its mainstream counterpart. However, most of the additional pipes are of small diameter (DN20, DN40).
Somerkallio said these variables confirm the need for review at the individual ship level, although he added some general observations about tanker installations. No matter what solution the main system requires, the tail-tip cabin needs a different arrangement. You can consider using a separate UV or EC system at the stern, but you can also consider using a full-ship EC solution to ensure that the pump system separation time between the main system and the stern system is long. In the latter case, the “chemicals” produced in the safe area will be separately distributed to the Aft Peak Tank system.
Somerkallio pointed out that all types of EC systems produce hydrogen as a by-product, adding that the side flow option here is definitely more risk-averse: hydrogen can be extracted from the chlorine buffer tank through forced ventilation to trip the BWMS in the event of a ventilation failure.
Similarly, operators who prioritize maintenance should consider that although mainstream systems are in principle less complex, meaning fewer components, two separate BWMSs may be required: overall, the number of components will be more. In addition, Foreship said that mainstream systems it evaluates are generally more prone to deterioration over time than sidestream systems.
In contrast, both systems require regular filter replacement, but side-flow pumps and blowers require attention after 2500 hours. Although most of the work can be done by the crew, Somerkallio said that a comprehensive assessment of maintenance in this area is still to be carried out.
When the shipowner faced the reality of the retrofit technology, he suggested that Foreship’s detailed feasibility study showed that any beauty of BWMS may be very strong in the eyes of bystanders.
According to Abdel Latif Wahba (Bloomberg), Egypt is expected to finalize an agreement next week to compensate the giant ship that blocked the Suez Canal in March.
Ismailia, June 23 (Reuters)-The owner of a giant cargo ship that blocked the Suez Canal in March and the insurance company reached an agreement in principle in a compensation dispute…
Author: Captain John Conrad (gCaptain) In November last year, Forbes published a series of articles claiming that Biden will make the most critical nominations for the future of our oceans, climate, and…
Necessary cookies are absolutely necessary for the normal operation of the website. This category only includes cookies that ensure the basic functions and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the operation of the website and are specifically used to collect user personal data through analysis, advertising, and other embedded content are called non-essential cookies. You must obtain user consent before running these cookies on your website.
Post time: Jun-26-2021
