Silicon carbide membrane 

application in Ship washing waste water

Treatment of ship washing wastewater

According to MARPOL convention, the sulfur content of marine fuel in the four emission control areas (i.e. ECA area) of Baltic Sea, North Sea, North America and the Caribbean Sea of the United States shall not exceed 0.1% after January 1, 2015, and the maximum sulfur content of marine fuel in other sea areas except emission control areas shall not exceed 0.5% (previously 3.5%) after January 1, 2020.

The 72nd session of the Marine Environmental Protection Committee (MEPC 72) of the International Maritime Organization (IMO) pointed out that the loading of non-conforming fuel oil is prohibited unless the ship is equipped with an equivalent system approved in accordance with Article 4.1, which has the same effect in reducing Sox emissions as the use of compliant low sulfur fuel oil. The equivalent system here is that the ship is equipped with desulfurization system (scrubber).

China's Ministry of transport also plans to expand the coastal emission control area, planning to expand from the Pearl River Delta, Yangtze River Delta, Bohai Rim (Beijing, Tianjin and Hebei) to 12 nautical miles of China's coastal waters, as well as Hainan waters; in terms of control requirements, from January 1, 2019, ships sailing and berthing in coastal control areas should use fuel oil with sulfur content ≤ 0.5% m / M; from January 1, 2020, ships should use fuels with sulfur content less than or equal to 0.5% Fuel oil with sulfur content less than 0.5% m / M and fuel oil with sulfur content less than or equal to 0.1% m / m shall be used for ships navigating in coastal control areas.

At present, there are three kinds of countermeasures for shipowners

      1. Use low sulfur fuel with 0.5% sulfur content

      2. Use clean fuel, such as LNG, etc

      3. Installation of desulfurization system (scrubber) on ships.

      The simplest way is to switch directly to low sulfur fuel oil with a sulfur content of 0.5%. The price of low sulfur fuel oil is high, and the use of low sulfur fuel oil will cause heavy fuel cost burden to shipowners. And industry insiders believe that it may be technically feasible to produce enough marine fuel with sulfur content of 0.5% in 2020, but it is not economically feasible for refineries, which will lead to a shortage of supply.

       Using clean fuel, building LNG powered ships or retrofitting existing ships to use LNG power is the direction of future development. However, at this stage, the transformation cost is huge, the equipment supporting system is expensive, and the safety is controversial. At the same time, the port filling network in the world is generally imperfect, which affects the normal operation.

       Scrubber desulphurization installation, can continue to use the high sulfur fuel, through the system to process the vessel containing the SOx emissions, with high desulfurization efficiency, equipment advantages of strong adaptability, although the modification cost is not low, but can be offset, the economic benefits of high and low fuel price difference later operation and maintenance costs are lower and weakness is needs certain space, the current washing tower model there are three main types: open system and closed system and mixed system.

The open desulfurizing tower is suitable for seawater area. The weak alkaline seawater is used to neutralize and absorb the tail gas containing sulfur oxides and nitrogen oxides, and to wash the smoke and dust in the tail gas. The washed water is discharged outboard after the pH value test meets the standard.

The notice of the maritime administration of the Ministry of transport on standardizing the supervision and management of the ship's air pollutant emission control area stipulates that the discharge and treatment of water pollutants generated by the ship's tail gas post-treatment device shall meet the requirements of relevant regulations.

It is forbidden to discharge washing water from the open exhaust gas cleaning system in the inland river control area, the port water area in the coastal control area and the Bohai Sea water area, and the requirements for the prohibition of the washing water of the open exhaust gas cleaning system in the waters of other coastal control areas will be announced and implemented in due time.

It is forbidden to discharge the washing water residue of the waste gas cleaning system into water or burn it on board. The ship shall record the washing of the waste gas cleaning system truthfully.

It can be seen that the use of open desulfurizing tower has been prohibited in the port waters and Bohai waters of ECA in China. If an open desulfurization tower is installed in the above areas, the conversion operation procedure of high sulfur oil for low sulfur oil shall be carried out in advance.

The closed desulfurization tower is suitable for fresh water and harbor waters. Alkaline chemicals are mixed into the washing water to wash the ship's tail gas. The washing water in the desulfurization tower is discharged into the collection tank on board, waiting for shore or a third party to receive.

The hybrid desulfurization tower combines the advantages of open desulfurization tower and closed desulfurization tower. It can be directly washed by seawater and discharged directly after passing the test. It can also be collected on board after washing in fresh water and harbor waters with alkaline chemicals.

Silicon carbide membrane system as a desulfurization tower washing wastewater treatment device has the following obvious advantages:

1. Ensure compliance with IMO emission regulations;

2. Reduce the sludge volume and treatment cost of the scrubber;

3. High precision membrane filtration technology with stable and durable effluent quality;

4. Modular system design for convenient and flexible installation;

5. At present, Wartsila has adopted silicon carbide membrane system as the standard treatment device for washing wastewater of desulfurization tower;

Silicon carbide membrane system has application value in the treatment of ship sewage and domestic sewage combined with other processes.