Marine Exhaust Solutions: MES EcoSilencer® FAQs

What is a Marine Exhaust Solutions EcoSilencer®?
With first applications of scrubbing technology experienced in 1998, the now patented EcoSilencer® design brings well proven, reliable, and low maintenance principles of seawater scrubbing systems, used for decades by land based applications for SO2 emission reduction, to the shipping industry. The system has undergone 6 years of testing and shipboard trials that have proven the systems ability to dramatically reduce SO2 in exhaust emissions, remove soot particulate, and reduce exhaust noise.

How will this system benefit the owner/operator?
The MES EcoSilencer® will make your ship engine, auxiliary engine or boiler emit an exhaust plume that, meets the toughest local pollution regulations, and produces very little noise or smell to bystanders. The process can generate these benefits while burning heavy fuel (HFO), without forcing you to burn expensive alternatives in designated Sulphur Emission Control Areas (SECA).

What level of sulfur dioxide removal is achievable?
Using seawater as the scrubbing solution, we have found that up to a 95% removal of sulfur dioxide in the exhaust gas is possible. See the Payback & Performance FAQs for details.

What sort of equipment can benefit from this system?
Our equipment can be custom designed for your particular combustion source, whether it is a Diesel engine, oil-fired boiler, or waste incinerator. The small footprint of our system makes it practical for almost any shipboard installation.

What does the system do to exhaust?
Hot exhaust is routed through a central chamber where it passes though our innovative patented exhaust chamber, interacting with seawater. Since many gases (such as HCl or SO2) are water soluble, this is an effective means to clean exhaust gas. The water is treated and recirculated within the system. In fact, similar processes are used in large-scale plants to scrub emissions from most of the world's shoreside coal and oil-fired electric generating stations. Our system is the first to be practically implemented on a small shipboard scale.

What happens to the scrubbing water?
Seawater is our preferred scrubbing solution. Since seawater already contains 900 mg/l of sulfur as a natural constituent, it makes an ideal solution to remove gases from exhaust. Sulfur from combustion of heavy fuel can be converted into natural sulfate within our system (sulfate is a common constituent in wine, drinking water, seawater, even dried apricots), and can be safely, and soundly released to the environment. Before discharge, the water is filtered and treated to remove any solid particles, hydrocarbons that was collected from the exhaust.

What makes this system unique?
The system we have developed uses a patented method of passing the exhaust gas through sea water which ensures that the maximum contact time is achieved with the smallest cost in backpressure, and in the most compact package.

What particle size does this remove from exhaust?
We have made measurements of exhaust particulate concentrations using a filter with a pore size of 0.47 micron. With these filters, we have found up to 80% removal of particulate by weight. The technique is, however, known to be most effective at removing larger particles.

Is there any impact on the NOx concentration?
Under normal operation with seawater as the scrubbing solution, a NOx removal between 5-15% is achievable. This is variable based on water temperature, and salinity.

10.

What backpressure does the scrubber generate?
For operation with a diesel engine, the system can be operated at back-pressure levels between 75 to 150 mm-H2O. Backpressure is monitored by a differential pressure transducer, and is used as an important parameter in the electronic controller for the system.

11.

With the sulfur continuously being washed out into the circulating seawater, how do you eventually get rid of the sulfur, and will not the seawater after a short time be a sulfuric solution?
Sulfate, or SO4 is a natural component of seawater. Removing SO2 from exhaust gas into seawater produces both SO4 and SO3 in the water. By ensuring sufficient oxidation of the wastewater, the sulfate resulting from exhaust scrubbing can be released overboard through a cyclonic filtration system without negative environmental impacts.

12.

A wet exhaust system must generate a lot of wastewater. Is this so?
Our system design ensures that water used in the scrubbing process is conserved. We maintain the temperature cycle of the exhaust gas through our unit to keep the moisture loss to the exhaust gas at a minimum. The wastewater is divided into two streams. One, which contains dewatered solids in an amount of less than 200 g/MWh, and another which is filtered and treated seawater with a small amount of dissolved sulfate. The sulfate concentration in this water stream is indistinguishable from background sulfate variations within a few meters of the outlet.

13.

What about scrubbing water temperature?
Practice demonstrated that for 4.8 MW engine(s) shaft output system, the temperature of returning scrubbing water is 40-45°C. In the process of water exchange, the scrubbing inlet water temperature is maintained at 20-25°C. For a larger system, returning scrubbing water is cooled in a titanium plate type heat exchanger to maintain the very same temperature balance.

14.

Is it possible to eliminate the need for ANY wastewater outflow?
Yes. It is possible, not practical for all installations, to incorporate a limestone or Soda Ash addition system that will cause salts and gypsum to be collected in the system. The salts would be stored and disposed of safely onshore. In order to operate such a system, the user would have to provide a feedstock of approximately 8 kg/MWh of Limestone while burning 1.5% Sulfur Heavy Fuel.

15.

With such a cold exhaust gas, will not the SO2 corrode the exhaust pipes after the EcoSilencer®?
MES EcoSilencer® System removes majority of the SO2 from the exhaust gas and the acid condensation in the stack is considered to be less of a problem than in "hot" exhaust systems. However, one needs to remember that EcoSilencer® is a wet type scrubber and to fully protect exhaust system against corrosion, it is a good practice to use adequate corrosion resistant materials or liners.

16.

The seawater that comes from the EcoSilencer® after washing the exhaust may be expected to be very corrosive, what pipe-material are you using?
Marine grade GRP is used as piping material throughout the system for low temperature sections. SMO 254 or similar material is used as piping material for hot temperature zones normally confined to the areas in close proximity to an EcoSilencer® itself.
The above will prevent damages to the GRP piping when an EcoSilencer® would need to operate temporarily in dry silencer mode.

17.

A clarifier filters the dirty seawater, and you may easily have to remove a very large amount. What type of clarifier do you propose for this job?
We have based the system on a two-step clarification. The first stage clarifier is a hydro-cyclone type in large systems, which will remove particulate from water that is being recirculated through the scrubber, giving several passes through the clarifier. In smaller systems, this can be an automatically washed screen filter. The concentrated water/soot mixture from this first clarifier can then be treated in one of two ways;
a) It can be processed through a centrifugal separator to produce concentrated sludge stored in a system settling tank, or
b) The waste water can be delivered to a ship sludge tank, allowing the particulate to settle out,
The concentrated sludge from either of these options can be disposed ashore, or be burned with oil in the ship's oil-fired boiler. This latter option would result in a system with no solid waste produced, since diesel soot is largely made up of unburned hydrocarbon and carbon.

18.

Can the seawater with its contents of S be pumped straight overboard, after it is clarified for soot?
Once the wastewater has been cleared of soot and hydrocarbons, it is a solution having higher than ambient sulfate, but this is a naturally occurring component, and not considered an ocean pollution hazard. Before overboard discharge, the water must be passed through the ship's existing bilgewater treatment system, or a stand-alone system supplied by MES to remove any residual hydrocarbons.


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