What Are Diesel Exhaust Scrubber Systems and How Do They Work?

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Diesel engines release harmful components into the environment that contribute to climate change. Exhaust scrubbers reduce pollution by filtering gases through a liquid (usually water).

Open loop scrubbers utilize seawater as their scrubbing medium. Being alkaline in nature, sea water absorbs sulfur from exhaust gas forming sulfuric acid which serves to clean it further.

What is a Scrubber?

Scrubbers are air pollution control devices used to remove particulate matter and gaseous pollutants from industrial exhaust streams. Their classification depends upon their usage of scrubbing liquid, the types of pollutants targeted, and how they interact with their environments during scrubber processes.

Particulate dust scrubbers use water spray or multi-vane scrubbing mechanisms to target and collect fine particles that pose threats to the environment, before blowing them to a sump for disposal. Meanwhile, chemical gas scrubbers use an alkaline scrubbing liquid to neutralize chlorine and ammonia found in process exhaust streams by stripping away their acidic components – and so do both Particulate dust scrubbers and Chemical gas scrubbers.

As companies push towards reduced sulfur caps, many are searching for ways to minimize harmful contaminants and remain compliant. A reliable scrubber system combined with quality mist eliminators offers one effective means of eliminating harmful gases, particulate matter and odors from process exhaust streams.

Scrubber Technology

Scrubbers remove SOx and PM from diesel engine exhaust by passing it through a liquid. This scrubbing liquid may include sea water, chemically treated fresh water or dry substances like alumina and silica for effective removal of pollutants.

The scrubber system includes piping, scrubbers, pumps, coolers and tanks; many of the parts shared across multiple scrubber systems. Scrubbing liquid is fed into each scrubber using either blower or fan systems and flow rates vary dramatically depending on its size and source of pollution. Spray nozzles disperse this fluid throughout the gas stream to disperse it further into its surroundings (venturis or packed beds may also help).

Scrubbing processes produce waste products that need to be managed responsibly, such as mercury removal. Mercury is toxic and must either be processed into usable form or placed in designated hazardous waste landfills; therefore this must be considered when selecting scrubber technology. Other pollutants, like particulate matter and acids may produce similar waste that must be dealt with appropriately.

Scrubber Principles

Exhaust scrubber systems combine multiple techniques to remove toxic and corrosive compounds from exhaust gas emissions, and the primary components of such systems include:

Engine and boiler exhaust gases enter a scrubber to be treated with an alkaline scrubbing solution such as seawater or chemically treated freshwater. Once used, this waste stream contains both the scrubber’s waste solution as well as any unavoidable particulate matter from its use, which are washed off using wash water before discharging into the sea.

Fan or blowers provide motive force for moving dirty gas through a scrubber, while piping systems carry the cleaned gas to its final destination. Inlet gas distributors and flow control dampers enable adjustment of throughput rates while spray nozzles or packed towers evenly distribute scrubbing liquid across its cross section to maximize surface area for gas-liquid contact, thus effectively neutralizing pollutants from exhaust gas emissions.

Scrubber Installation

Exhaust gases from diesel engines and boilers release harmful substances into the air that are detrimental to human health, potentially causing eye and nose irritation, headaches, drowsiness or even loss of consciousness. Scrubbers help mitigate these dangerous chemicals.

Wet scrubbers use liquid to scrub exhaust gases through, collecting and dissolving pollutants such as water or alkaline solutions that capture and dissolve pollution in exhaust gas emissions. Packed beds inside wet scrubbers ensure maximum contact time between the exhaust gas and scrubbing liquid for effective pollutant removal.

Scrubbing liquid is then washed off the vessels and discharged back into the sea after treatment, although care must be taken not to install scrubber-equipped ships near conservation areas due to marine life safety considerations. Though installing and retrofitting these systems is expensive, their effectiveness in eliminating sulphur oxide emissions meets stringent new IMO 2020 regulations making this an invaluable investment for many ships.

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