Ballast water is the most frequently cited cause of the introduction and transfer of non-indigenous species (NIS) into waterways. Ballast water management strategies, coupled with stringent regulation, aim to prevent, reduce or eliminate the transfer of harmful aquatic organisms and pathogens through the control and management of ships' ballast water and sediments. Ballast water treatment systems are a proven approach to limiting the introduction and transfer of NIS. Technologies used for treating ballast water are typically identified as solid-liquid separation, disinfection or some combination of the two.
The Marine Environment Protection Committee (MEPC) of the International Maritime Organization met February 2004 and adopted a new world Ballast Water Convention that will take effect 12 months after ratification by 30 member states representing 35 percent of the world's gross tonnage. The Convention is divided into articles and, more importantly for the development of ballast water treatment technologies, an annex that includes technical standards and requirements in the regulations for the control and management of ships' ballast.
All ships including submersibles, floating craft, FSUs and FPSOs, are to manage their ballast water in accordance with an approved Ballast Water Management Plan and record such management in a Ballast Water Record Book. Initial implementation was scheduled for 2009 adoption, with a 2012 / 2014 / 2016 staggered enforcement based on a ship's size and date when construction begins. Implementation is still pending, waiting ratification by the 30 member states. Once triggered, the implementation will be compressed at the front end to meet the same 2012 / 2014 / 2016 staggered enforcement. All ships in service must use ballast water treatment by 2016. The ballast water treatment market is targeted toward retrofitting equipment for existing ships / vessels and providing equipment for newly built ships / vessels.
These two distinct market segments have subtle differences, yet share common purchasing decision factors. While CAPEX is the key factor for new builds and total cost of ownership is the most critical factor for retrofits, operational ease, footprint, ability to meet specific vessel requirements, ease of installation and maintenance are important factors for both market segments. As a result, modularly based ballast water treatment systems present a competitive advantage for the retrofit and new build market, especially tank ships with high volumes of ballast water and explosion-proof, application-specific requirements.
Tank ship ballast water requirements
Oil, gas or chemical tank ship ballast water systems handle higher volumes and flow rates than many other vessel types. These higher flow rates require larger and more powerful ballast water treatment equipment and accessibility for routine maintenance and repair.
Tank ships are designed to carry hydrocarbons in bulk. The cargo tanks carrying the hydrocarbons are by definition hazardous areas. While not intended to contain hydrocarbon gases or liquids, adjacent spaces to these tanks, including ballast tanks and the pump room, must be designed to meet the requirements for a hazardous area. As a result, the installation of ballast water treatment equipment must meet classification society hazardous area rules. Hazardous area rules establish additional requirements on the type of electrical equipment and place restrictions on piping connections to areas where hydrocarbons may be present.
"American Bureau of Shipping (ABS) Rules for Building and Classing Steel Vessels" set limitations on how piping can be run between hazardous and non-hazardous compartments. The regulations imply that all ballast water treatment system components must be placed in hazardous areas only. This is often both impractical and inefficient. Given the system's electrical power requirements, the need for accessibility to carry out routine maintenance and repair, as well as other factors, it is preferable to install the components in a non-hazardous area such as the engine room or an auxiliary machinery space.
Since there are no specific rules governing communication between hazardous and non-hazardous spaces for a ballast treatment system, and in the absence of such rules, analysis and a comprehensive risk assessment should be conducted to demonstrate that the installation of a ballast water treatment system meets or exceeds comparable safety standards established for other systems that permit communication between hazardous and non-hazardous spaces.
The ABS "Guide for Risk Assessment for the Classification of Marine-Related Facilities" provides an approval process for such a situation: "....where a design is being proposed on the premise that it provides equivalent protection against the risks addressed by the ABS Class Rules, rather than by strict compliance with existing prescriptive classification Rules."
An ABS technical review team reviews a risk assessment and concludes if the proposed arrangement provides an equivalent level of safety and is suitable for classification.
The importance of a modular ballast water treatment design
Once a proposed ballast water treatment arrangement is approved for hazardous classification, installation can then be undertaken. The system should be designed to minimize the rearrangement of existing shipboard equipment and ensure system components are readily accessible for operation and maintenance. As such, a compact, modular ballast water treatment system design is required for installation on board an existing vessel.
In the first quarter of 2008, a BALPURE® ballast water treatment system from Severn Trent De Nora was installed for testing on SeaRiver Maritime, Inc.'s S/R American Progress, a 46,000 deadweight ton, double-hull product tanker. ABS provided the classification society oversight and acceptance role for this installation. The double-hull tank ship arrangement has 14 cargo tanks and 2 slop tanks. The double-hull, segregated ballast capacity is 19,000 cubic meters. The ballast is handled by two ballast pumps, each rated at 975 cubic meters per hour. The cargo and ballast pumps are located in a traditional pump room just aft of the cargo tanks and forward of the machinery space.
For this installation, the BALPURE system was separated into six components and installed in available space, eliminating the requirement to relocate other ship equipment:
- Electrolyzers
- Control Panel and transformer/rectifier
- Hydrogen separation
- Booster pumps
- In-line analyzers
- Sulfite addition
The BALPURE system was sized for 2,000 m
3/hr hour ballast flow.
The BALPURE system uses electrolytic technology to generate a biocide on demand. The BALPURE system generates biocides, meters and analyzes the residual level of both biocides and neutralizing agents, logging the performance of the overall ballast water treatment system for compliance and reporting requirements. As a result, the use of hazardous chemicals is not required. Modifications are minimal to the existing ballast water system, making the BALPURE system ideal for retrofit additions of ballast water management systems aboard tankers.
BALPURE is used during ballasting to filter and disinfect incoming seawater and during de-ballasting to neutralize residual oxidant in discharged seawater. During ballasting, a side stream of main flow is used to generate oxidants, and the main flow is filtered to return silt/sediments and large organisms back to the uptake location. Oxidants are injected back into the main line and an analyzer / data logger is used to monitor / control residual oxidant. TOC is monitored to predict uptake ballast water oxidant demand levels and accurately produce the required biocide for each location. During de-ballasting, sulfite is injected into the main de-ballast line to neutralize residual oxidants with an analyzer / data logger used to control and verify effective neutralization. The BALPURE system also maintains a residual oxidant until final de-ballast.
The BALPURE system can accommodate increased flow rates by expanding the base model and using larger electrolytic cells to generate greater quantities of the disinfectant required to treat the higher flow rates. The operating and capital cost implications of replication of smaller units are eliminated when the system is fully integrated to the ship's specific needs.
Other competitive ballast water treatment systems will simply replicate their base model design in order to treat increased flow rates, leading to an inefficient use of space and increased costs and system complexity.
Testing and verification
As a result of this assessment, testing and installation aboard the S/R American Progress, the vessel with the BALPURE system was authorized earlier this year by the California State Lands Commission to discharge treated ballast water into the state's water. The ship may continue to discharge treated ballast water with the BALPURE system as long as the vessel remains in the United States Coast Guard's Shipboard Technology Evaluation Program and operates in accordance with its specific conditions.
The BALPURE system has received Basic Approval, March 2010 (MEPC 60) and has been recommended for Final Approval by October 2010 (MEPC 61). Type Approval is projected for completion in early 2011.
For more information, e-mail info@severntrentservices.com.
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