INFORMATION FOR BASIC APPROVAL OF ACTIVE SUBSTANCES USED BY SPECIAL PIPE BALLAST WATER MANAGEMENT SYSTEM (COMBINED WITH OZONE TREATMENT)
This system employs a disinfection method which falls under the category of the in-line type to be installed in the initial ballast line for taking the ballast water. A complex of mechanical treatment by means of slit plates called “special pipe” and a chemical treatment by Active Substance. Ozone, heightens the disinfection effect for organisms.
The maximum Ozone feeding ratio to the ballast water of this system is 4 mg/L. Also this system is designed to store the treated water in the ballast tank at least 48 hours. Ozone is produced by converting a part of oxygen, as raw material, by the silent electric discharge. Since Ozone is not commercially prepared using additives, storing it on board is not required. It can be produced at any time when required in certain quantity by using of a generator provided on board. Therefore, the system can be handled on board very easily. The generator installed on board can quickly respond to any unforeseen inboard accidents and is assured to be safe.
1.1 System configuration
Configuration of the system is shown in Figure 1. Its main treatment process employs a disinfecting compound unit of mechanical treatment by means of slit plates and chemical treatment using Ozone. A pre-treatment unit, gas/liquid separation unit and discharge unit are also integrated with the main unit for the improved treatment performance, safety inboard, and environmental precaution against discharge. That is, the system is composed of four treatment processes, each of them is described below.
1.1.1 Pre-treatment unit
Pre-treatment is required for preventing blockage of the disinfecting unit.
1.1.2 Disinfecting unit
Disinfecting unit is composed of mechanical treatment and chemical treatment with the generated Ozone.
1.1.3 Gas/liquid separation Unit
De-aeration is a gas-liquid separation process to prevent Ozone without reaction from flowing into the ballast tank. An Ozone discharging unit to handle the de-aerated Ozone in the gaseous phase is also required.
1.1.4 Discharge treatment unit
The system is designed to decompose oxidant remaining in the ballast water at the time of discharge. Active carbon, etc, act to decompose the residual oxidant to 1/10.
Figure 1. System Configuration
1.2 Conception on onboard installation
This system can be installed by using the existing ballast line. In order to avoid human errors by operators, the equipment is integrated within the ballast remote control console in view of importance to operability.
This system plans to be installed on an existing container ship of 60,000-ton class in August 2006. Figure 2 outlines a piping system diagram.
Figure 2. Piping System Diagram
1.3 Ozone generator
1.3.1 Components of Ozone generator
The Ozone generator is composed of Ozone generating unit, Ozone control panel and other components. Functions of each unit composing the Ozone generator are shown in Table 1.
Table 1. Components of Ozone Generator
|Ozone generation process
||Composed of the Ozone generator to generate Ozone and the power supply unit (PSU) to supply electric energy to the Ozone generator. Multiple electrodes are contained in the Ozone generator to convert a part of oxygen in the gas to Ozone. The power supply unit (PSU) converts the power type from commercial frequency and low voltage to medium frequency and high voltage most suitable to Ozone generation.
|Ozone control panel (Power Instrumentation panel)
||Adjust the power output of PSU and quantity of Ozone to be generated, monitors the status of gas and cooling water around the Ozone generator, interlock the system to control the system or protect the equipment and for safety, and transfer signals to mad from the central console. Receives all the power required for PSU and instruments and supplies the power to each equipment and instrument.
||Includes the emergent shut-off valve, safety valve, Ozone monitor, Ozone leakage monitor, dew point meter, Ozone flow meter, temperature indicator, pressure indicator, etc. Located online or around the Ozone generator.
1.3.2 Peripheral units of Ozone generator
To ensure normal operation of the Ozone generator, air as raw materials, cooling water and other utilities should be properly supplied. Peripheral units required for the supply of utilities are shown in Table 2.
||Functions of Peripheral Units of Ozone Generator
||Function of Ozone Utility
||Pressurizes and compresses the air to generate oxygen efficiently. When used for generating Ozone, an oil-free air compressor should be used.
||Used to remove dust from dry oxygen supplied to the Ozone generator.
|Oxygen Generator (PSA) Unit
||Concentrates the compressed air supplied from the compressed air by pressure swing (PSA; Pressure Swing Adsorption) to obtain oxygen. Removes moisture at the same time to supply dry oxygen more than 90% to the Ozone generator.
|Cooling water supply unit (Chiller Unit)
||Used to remove heat generated in the Ozone generator. Cooling water supply unit for this system is an air-cooled chiller unit, etc. using coolant. Cooling water is ion exchange water cooled by being circulated in a closed loop. To release the pressure in the cooling water line, a head tank may be installed in the cooling water line.
1.4 Safety measures for Ozone generator
To completely eliminate the Ozone leakage, which is harmful to human health, the following measures are taken for the safety of the Ozone generator:
1.4.1 Provision of leaking Ozone densitometer
Ozone leakage from the Ozone generator and Ozone piping line is harmful to human body (crew). Leaking Ozone densitometers are provided around the Ozone generator, ballast tank air vents, and other places to monitor Ozone leakage constantly. The system is designed (controlled) to raise the alarm if Ozone leakage is detected, and Ozone generation discontinues and supply of the Ozone gas shuts off depending on the situation
1.4.2 Emergency stop
In the event that the Ozone generation should be put in emergency stop while the ballast water is treated by Ozone on board, it is designed to stop the Ozone generation immediately from the remote ballast control console or others.
1.4.3 Fail-safe system
If a power trouble or failure arises in the equipments, the fail-safe system is activated.