Ship Scrubber Unit (2)--MarinSmart Expert Committee

Scrubber?tower residue definition and treatment

Scrubber tower residues are sulfates, ashes, metallic substances and hydrocarbons separated from the ship's exhaust gas scrubber water treatment process, etc. Their forms range from liquid to solid, and the specific classification depends on the regulations of each port state (the International Maritime Organization has not yet issued a unified nature of scrubber tower residues and treatment methods).

European ports have better supporting facilities for receiving wash water and residues from exhaust gas cleaning systems, and ships can use the ship waste disposal application form for declaration before arriving at European ports.

At present, the washing tower residue reduction technology is mature, and ships should reduce the washing tower residue in advance, so that not only can reduce the cost of collecting and treating the residue on ships, but also once the volume of the washing tower residue is reduced and compressed to make it solid, it will be easier to sort the reduced treated washing tower residue and thus choose a more appropriate treatment method.

Ship incinerator can burn the waste oil and most of the solid waste generated by the main engine, sub-engine, oil-water separator and each oil pump, so the incinerator slag composition is more complex than the scrubber tower residue, and incinerator slag treatment has been included in MARPOL Convention Annex V (Prevention of Pollution by Garbage from Ships Rules), so we can completely scrubber tower residue in accordance with the provisions of MARPOL Convention Annex V for treatment.

Treatment of ship?scrubber?tower wastewater

After the seawater or lye of spraying?scrubber?tower absorbs the SO2 and particulate matter PM in flue gas, it mainly generates waste liquid containing soot, sulfate, sulfite, etc. in colloidal suspension, and its pH value is below 5.7, which is weakly acidic. Therefore, this kind of wastewater must be properly treated and discharged only after reaching the standard, otherwise it will cause secondary pollution. The wastewater treatment process is roughly divided into neutralization, heavy metal removal, flocculation, concentration, clarification and sludge treatment.?Neutralization is to use alkaline substances such as Ca(OH)2 as neutralizing agent to add into the?scrubber?waste water to neutralize the acidity of the wastewater.

The wastewater containing metal sulfide enters the flocculation tank, adding certain coagulant to make the fine sediment flocculate and settle; then the flocculated and settled wastewater enters the sedimentation tank for solid-liquid separation; part of the separated sludge is sent to the sludge treatment system for dewatering treatment, and the other part is returned to the neutralization tank to provide crystalline nuclei for flocculation. The pH value of the sedimentation tank effluent is high and needs to be treated to meet the standard before discharge.

Discharge water parameters such as pH (with temperature compensation), polycyclic aromatic hydrocarbons (PAH), and turbidity are continuously monitored and recorded by discharge water analysis instruments according to time and vessel location to ensure that the FGD tower wash water discharged into the sea does not pose a hazard to the marine environment. These data must be retained on board for not less than 18 months and audited and verified by the port state and flag state.

Information from?the MarinSmart platform?shows that

Some countries and regions believe that untreated open scrubber water contains heavy metals, aromatic carbon mixtures and carbon soot particles, which can pollute the discharge waters and contain toxic substances that can degrade the marine environment. For environmental or political purposes, these countries and regions have issued bans on the discharge of FGD scrubber water in regulated waters, which is equivalent to a ban on the use of open FGD towers, while ships with hybrid and closed-loop FGD towers must also switch to "zero discharge mode".

The Suez Canal explicitly bans open scrubber towers:?approximately 8.3% of global maritime trade and 25% of containerized cargo sails through the Suez Canal. The Suez Canal Authority (SCA) declares that under no circumstances shall effluent from exhaust gas cleaning systems be discharged into the Suez Canal during the passage of ships through the canal.

On November 18, 2019, a Marshallese flagged tanker was issued a maximum fine of €50,000, or approximately RMB 390,000, by the Hamburg authorities in the port of Hamburg for violating the ban on the use of open-loop?scrubber?equipment. According to the requirements, ships are strictly prohibited from discharging wash water into the Elbe River and the Port of Hamburg. Ships equipped with open scrubber towers should switch to low sulfur fuel oil in time. Closed loop wash water and solid wash waste from ships can only be discharged to the port reception facility in Hamburg on a fee basis.

The use of open FGD equipment is prohibited in the following countries (ports):

China, Belgium, Germany, Estonia, Finland, France, Gibraltar, UK, Ireland, Italy, Latvia, Lithuania, Norway, Portugal, Russia, Singapore, Sweden, USA, UAE, Malaysia, Suez Canal, etc.

Although the ban is aimed at open FGD towers, but at present from some shipowners' position, the impact of the ban on the whole FGD tower market is not big, and does not affect the market structure of FGD towers, open FGD towers still in the market absolutely dominant (about 80% of the total), mainly because the fuel consumed by ships sailing at sea is more than 90% of the whole operation process, the ship in the port The amount of fuel consumed in the water is much lower than at sea, and where open FGD towers are not permitted, the choice of low-sulfur fuel for ships calling at such ports has an extremely limited and economically viable impact on costs.

Ships are advised to contact their agents before calling at ports in these countries to ensure that they are not subjected to large fines for FGD tower scrubber water discharge problems.

Wastewater resource treatment:?The reasonable treatment of wastewater should be able to recover and comprehensively use the sulfates in the wastewater, so that the waste can be resourceized. For example, Japan and Germany in wet flue gas desulfurization, the successful conversion of sulfate in wastewater into gypsum; there is also the conversion of sulfate in wastewater into high concentration, high purity liquid SO2, as a raw material for the production of sulfuric acid.

Harmless theory of wastewater:In the?process of desulfurization, SOx gas is absorbed by seawater or alkaline water spray. Through a series of reactions in the?scrubber?tower, SOx is eventually converted to sulfate, which is a natural component of seawater, so the?scrubber?tower wash water containing sulfate is said to be harmless to the ocean. The small amount of sulfate produced in the FGD tower is insignificant and benign compared to the amount of sulfate present in the ocean (the ocean is the earth's natural reservoir of sulfur, which plays a key role in the sulfur cycle). After testing by a leading classification society, it was concluded that the pH of the FGD tower discharge water returned to that of seawater within 2-4 meters of the discharge site. As a 2012 study by the Danish Environment Agency showed, even in semi-enclosed marine areas, the acidifying effect of a ship equipped with a?scrubber?tower on the discharged water is negligible.

The price difference between high and low sulfur oil, the cost of?scrubber?tower, the adjustment of ship routes and the emission effect of the ship after the installation of?scrubber?tower will affect the shipowner's attitude towards?scrubber?tower, how to get the maximum benefit with the minimum cost is the starting point of the shipowner's choice to install?scrubber?tower is also the focus of his attention.