How do scrubbers work

The revision allows for calculation or modelling to verify the discharge of wash water pH at a point of 4 m from the point of discharge.

Wet scrubbers are good at removing particulate matter and soot which although not currently regulated for specifically are likely to be so in future. Typically a scrubber will remove at least kg of particulate matter for every tonnes of fuel oil burned and possibly more depending on how much wash water is used.

These solids must be removed before the wash water is discharged overboard and to conserve space the system should have a separation phase included that removes as much of the water as possible before sending the sludge to be stored for later disposal ashore. Scrubbers are increasingly being fitted to newbuildings but the majority now in operation have been retrofits.

The time for a retrofit is currently more than a typical scheduled drydocking meaning that extra lost earning days add to the capital outlay. Take up rates for scrubbers may be improved if flag states and others offer state aid or attractive financial deals.

So far aid has been limited to a small number of projects in Europe and some finance houses have begun offering schemes that assist with capital expenditure and which link repayments to savings made. The number of ships fitted with scrubbers is growing and with it the number of scrubber manufacturers. At the time when the first commercial system was fitted in , there were just a few organisations interested in the potential.

Today the number of makers active in the field exceeds 20 and newcomers are appearing regularly. Guides Show sub menu. Ballast water treatment.

Coatings and corrosion. Power, propulsion and turbochargers. Fuels and lubricants. Shipping and the environment. Navigation and the bridge. Safety and training. Collections Show sub menu. Internet of things. News categories Show sub menu. Ancillary Machinery. Ballast Water Treatment. A scrubber works by spraying a wet slurry of limestone into a large chamber where the calcium in the limestone reacts with the SO 2 in the flue gas.

There are some variations in design of scrubbers. For example, some scrubbers may use other chemicals such as lime or magnesium oxide to react with the SO 2 in the flue gas. How is SO 2 emitted through a coal-fired power plant? Coal is not a pure carbon; most coal contains other chemicals, including sulfur. Why does SO 2 need to be scrubbed? Emissions from automobiles and trucks, industrial processes, wood-burning stoves and forest fires, and surface mining and agriculture activities also contribute to the formation of fine particles.

Industrial scrubbers are divided into two categories, wet scrubbers and dry scrubbers. Both act in the smokestack and often use limestone, which chemically is a base, as a key ingredient because it reacts with sulfur dioxide and other acidic pollutants. Other chemicals, such as activated alumina which neutralizes hydrogen chloride gas, can be included to target other pollutants. Wet scrubbing can clean air, flue gas or other gases. A mixture of water and limestone, or other specifically targeted chemicals, is sprayed into the smokestack.

The mixture, or slurry, goes through a nozzle, or the polluted gas can be directed through a tube packed with the mixture. The scrubber can use water alone if the object is simply to remove dust particles. As the gases come in contact with the slurry, dust particles of many pollutants adhere to the water. They fall to the bottom of the stack where they can be removed. Sulfur dioxide, one of the most harmful pollutants, reacts chemically with the limestone and is trapped inside the particles, which can be filtered out.

Because pollutants can differ in their charge, scrubbers can be packed with a liquid that will bind most effectively to remove the contaminate from the gas. The gas exiting the scrubber is thus cleaner. Developments in wet scrubbers have allowed for increased efficiency in pollutant removal. One of the major developments has been to maximize the total surface of the liquid with which the polluted gas associates.

More surface area means that more of the contaminates can be pulled out of the gas. Another development in scrubbers has been increasing the mixture of the gas with the scrubber fluid. These aspirators agitate the solution and increase the mixing of the polluted gas and the liquid. The wet scrubber differs from the other different types of industrial scrubbers because the liquid-gas association increases the moisture level of the gas that is being expelled from the scrubber.

The increased moisture in the gas will create a visible cloud exiting the scrubber. Unlike wet industrial scrubbers, dry scrubbers do not utilize a liquid to absorb contaminants. Because of this difference, steam is not produced by the reaction, and a wastewater system is not needed. A dry industrial scrubber is composed of a reaction center where the sorbent or dry reaction material that absorbs contaminants is mixed with the polluted gas.

Also within the system is a material component that aids in the removal of the reaction product, which is the dry sorbent bound to the pollutant. Dry scrubbers are used primarily to remove acids found within gasses. The dry sorbent used to remove the acid from the gas is usually made of an alkaline slurry.