Since the “International Maritime Organization Ballast Water Convention” came into effect in September 2017, shipowners have been calling on a Finnish naval construction and marine engineering company to conduct an independent evaluation of its ballast water management system transformation plan.
In recent months, signatures have been added to the 2004 International Convention for the Control and Management of Ships’ Ballast Water and Sediments. This cannot conceal the fact that this has been banned by the International Maritime Organization (IMO) since its conception. The 52 states that have signed contracts with the IMO have exceeded the required 30, but only accounted for 35.1441% of the world tonnage, barely exceeding the 35% threshold required to trigger entry into force 12 months after approval. It seems that the legal “document” is imminent, but it is still not an easy task.
However, in 2016, the shipowner left the matter to himself, because he firmly believed that the best BWMS performance of existing ships urgently needed technical answers.
Foreship, a leading naval architecture and marine engineering consulting company, has recently been providing detailed recommendations on retrofit options, and the feasibility study covers single ships. Classification societies are evaluating different technical solutions and similar technologies provided by different suppliers for different types and ages of ships, and evaluating the overall installation work, installation location, and temporary and permanent structural modifications.
Olli Somerkallio, former head of the machinery department, explained that although the choice between systems will definitely be guided by cost, it is not easy to compare.
“We focus on the technical aspects of installation, which means room for equipment, plumbing and electrical compatibility,” Somerkallio said. “To obtain meaningful results, you need expertise in naval architecture, marine engineering, and ship behavior.”
The cruise ship sector’s ballast water flow rate requirements are usually below 500m3/h, leading shipowners to choose UV-based BWMS technology, which makes invasive species “infeasible” instead of killing them. However, as has been widely reported, the U.S. Coast Guard has not yet finally approved the UV test standards.
In addition, UV devices are not feasible for the larger 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 in water to cause a reaction with sodium chloride. The free chlorine produced kills bacteria and other microorganisms in the ballast tanks. In the deballasting stage, the chlorine content is measured and a neutralizer is introduced as needed.
Owners should note that the additional piping required by BWMS, related fittings and valves, and BWMS itself are all sources of pressure loss. Somerkallio suggests that which ballast pumps must have sufficient head pressure to solve them. He said that the future makes pressure loss analysis part of its feasibility study because sometimes it is necessary to upgrade the pump impeller or motor. He said: “In the worst case, the entire pump may have to be replaced.”
Somerkallio said that special consideration must also be given to tankers, because ballast water is carried out at the bow and stern at the same time. The ballast tanks at the stern are usually three-quarters full and are therefore vital to the unimpeded flow of the vessel. Here, the main ballast system pump is located in the cargo oil pump room (hazardous area), so it cannot be used to pump water to the stern peak tank in a safe area. The stern pump cannot be directly connected to the main BWMS.
A typical mid-range oil tanker may require the main flow of the ballast system to be 2000 m3/h, and it is divided into port and starboard ballast tanks. This can be solved by two BWMS with a capacity of 1000m3/h, or by connecting both pumps to a single BWMS of the same processing system. The individual demand for stern ballast water will be handled by general service pumps connected to smaller BWMS with a flow rate of 250-300m3/h (for example).
A recent Foreship feasibility study evaluated in detail two EC solutions provided by competitor manufacturers: one adopts EC in mainstream products; on the other hand, EC occurs in the side stream and “chemical substances” are introduced Ballast tank.
Somerkallio said that, in fact, mainstream systems are simpler, lighter, and smaller than lateral flow systems, and consume approximately 25% less electricity. However, he added that attributes related to installation, performance and safety can persuade a bias current solution.
“For example, according to a manufacturer, due to special electrode design and materials, its mainstream EC system can operate at extremely low salinity, but cannot operate in almost zero salinity water such as the Great Salt Lake. Such restrictions are not Suitable for bypass systems; if the salinity is lower than 15 PSU, stored seawater can be used.”
Compared with mainstream systems, lateral flow systems can also operate in colder water.
Again, the volume of the sidestream system may be twice that of the mainstream system, and the weight has increased by 60%, but Somerkallio pointed out that it is more important to ask where the additional BWMS takes up space. He explained that the forward movement of the mainstream system requires a larger additional deckhouse for two EC units and two filters, while the 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 number of pipes required for EC process separation required by the sidestream system is twice that of the mainstream system. However, most of the additional pipes are smaller in diameter (DN20, DN40).
Somerkallio said that although he added some general comments about tanker installations, these variables confirmed the careful scrutiny of the needs of individual ships. No matter what solution is required for the main system, the stern tank needs a different arrangement. You can consider installing a separate UV or EC system at the stern, but you can also use the EC solution throughout the ship, so you can ensure a long-distance pump system isolation between the main system and the stern system. In the latter case, the “chemicals” produced in the safe area will be separately distributed to the stern peak storage tank system.
Somerkallio pointed out that all types of EC systems produce hydrogen as a by-product, adding that this side-stream option definitely brings greater risks: in the case of poor ventilation, it can be extracted from the chlorine buffer tank through forced ventilation. The hydrogen tripped the BWMS.
Third, 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 the mainstream systems it evaluates are generally more prone to degradation over time than its mainstream servers.
On the contrary, both systems require regular filter replacement, but after 2500 hours, the side-flow pumps and blowers need attention. Although most of the work can be done by the crew, Somerkallio said that a comprehensive assessment of maintenance in this area is still in progress.
When the shipowner faced the reality of the modification technology, he said that the detailed feasibility study conducted by Foreship showed that any advantages in BWMS may be very strong in the eyes of bystanders.
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Post time: Feb-26-2021