This design has advantages of high efficiency in producing intense mixing flow and a high interfacial area for generating small bubbles to rapidly treat a large volume of ballast water. Microorganisms are killed by an appropriate mixed fluid downstream, whilst large organisms are killed by the high-velocity impact of the ejected flow. Specifically, a small amount of ballast water from the main pipe is pumped as the primary fluid through the ejector to produce a lower pressure in the suction chamber of the ejector, which absorbs ozone as the secondary fluid into the ejector and then ejects it into the downstream of the main pipe to clean the ballast water. However, ozone is no longer directly pumped into the ballast water but is absorbed and ejected into ballast water by an ejector (see Figure 2).
This system still employs ozone to kill the microorganisms. Figure 1 shows the diagram of the proposed ballast water treatment system in this work. In order to kill both large organisms and microorganisms, a new ozone treatment system needs to be developed. It is very effective to kill microorganisms, but not so at killing larger organisms.
In the conventional ozone treatment systems, ozone gas is directly bubbled into the water which decomposes and reacts with chemicals. Each of them has its advantages and disadvantages. The combination of them has two or more treatment methods to clear the ballast water.
Chemical treatment kills existing organisms with chlorine bleach and other toxic chemicals. Physical treatment uses heat, ultraviolet, sonic, and other radiations to kill organisms. Mechanical treatment uses fine filters to remove small immature young eggs of invasive species or uses high pressure jet to kill them. Currently, ballast water treatment solutions can be classified into four types: mechanical treatment, physical treatment, chemical treatment, and a combination of them. The worldwide concern over the potential harm of ecosystems from shipping ballast water has resulted in the development of a range of treatment systems to minimize these environmental risks. These foreign materials often include invasive exotic species that can cause extensive ecological damage and economic losses to aquatic ecosystems. However, the discharges ballast water usually contains a wide range of exotic species such as animals, plants, bacteria, and viruses, which may pose a threat to the local marine environment. When the ship reaches its destination, ballast water needs to be discharged and renewed for the next journey. Introductionīallast water is a huge amount of water (sometimes millions of gallons on a large ship) stored in the long-distance passenger and freight ships to provide momentum for ship stability. This study concludes that the RNG turbulence model is the most efficient and effective for the ballast water treatment system under consideration and simple change of nozzle shape can greatly improve the ejector performance under high back pressure conditions. Different turbulence models (including standard, RNG, SST, and ) with different grid size and bubble size are compared extensively and the experiments are carried out to validate the numerical design and optimization.
EJECTOR DESIGN CALCULATION SOFTWARE SOFTWARE
The ejector is particularly studied by a steady three-dimensional multiphase computational fluid dynamics (CFD) analysis with commercial software ANSYS-CFX 14.5. In this study, high-pressure water and air, instead of ballast water and ozone, are considered through extensive numerical and experimental research. Commonly, the liquid-gas ejector uses ballast water as the primary fluid and chemical ozone as the secondary fluid. In this communication, an improved ballast treatment system employing a liquid-gas ejector is introduced to clear the ballast water to reduce environmental risks. Currently, water ejectors are widely used in marine applications for ballast water treatment owing to their high suction capability and reliability. Shipping ballast water can have significant ecological and economic impacts on aquatic ecosystems.