Flue Gas Desulfurization

Dear Colleagues,

Methods of removing sulfur dioxide from boiler and furnace exhaust gases have been studied for over 150 years, since 1850. Today, SO2 removal techniques have become useful not only for their control but for the improvement of atmospheric air quality.

In general, FGD systems for SO2 control are categorized as “wet” or “dry,” with wet systems being the more common. Wet FGD systems are often called scrubbers, and enhanced SO2 removal from flue gas is achieved with an alkaline slurry or solution of lime mixed with magnesia. The final product is calcium sulfate dihydrate (gypsum) solid and/or calcium sulfite hemihydrate solid. Dry FGD systems, on the other hand, depend upon either a spray-drying process or a circulating fluid bed (CFB) process. These use slaked lime (Ca(OH)2) slurry as the reagent or dry hydrated lime (also Ca(OH)2) powder as the reagent.

A recent classification of (FGD) processes was set regarding how the sorbent is treated after SO2 adsorption. This includes once-through and regenerable processes. Once-through, or non-regenerable, processes utilize the sorbent as a beneficial by-product or dispose of it as waste. Non-regenerable FGD processes can be also divided into wet (aqueous solutions used to scrub SO2) and dry (dry sorbent injected into the flu gas stream) systems. On the other hand, the regenerable processes release the sorbed SO2 to generate other products such as elemental S, H2SO4, or liquid SO2.

The wet FGD scrubber is the dominant worldwide technology for the control of SO2 from utility power plants (approximately 85%) with dry FGD systems also used for selected lower-sulfur applications.

• Alternatives to FGD processes:

Some alternative methods have been applied to fuel to remove S from the fuel before or during combustion. Additives such as magnesium oxide or magnesium hydroxide have been applied for SO3 mitigation for oil-fired units. However, fuel additives have been less effective on coal-fired units. Hydrodesulfurization of fuel has also been used for treating fuel oils before use where lime is added to fuel during combustion in a fluidized bed at atmospheric pressure and ambient temperature. 

Another option with an environmental outlook has been seawater flue gas desulfurization (SWFGD) for coastal and naval applications. However, it has many drawbacks and technical limitations. 

• Waste and environmental problems associated with FGD:

All FGD processes (except for SWFGD) require large quantities of chemical sorbents and produce high volumes of sludge that require disposal ponds or landfill after being partially dewatered. In addition, these systems suffer from potential scaling and plugging of the scrubber system and auxiliary piping, requiring frequent shutdowns for maintenance and the use of replacement equipment for uninterrupted operation.

Drawbacks of seawater flue gas desulfurization (SWFGD), even though potentially successful, include the corrosive nature of the absorbent; low vapor loading capacity as the solubility of sulfur oxides (SOx) in seawater is lower than in limestone; high seawater flow-rate; and the large size of equipment to be deployed.

Therefore, the scope of this Special Issue is to provide an up-to-date insight to readers from both technical and scientific backgrounds on the developments within the field of FGD from technical and environmental points of view.  Researchers are invited to present their novel and unpublished works concerning:

• Technical changes and advancements in FGD systems;
• Alteration or upgrading of currently used system design;
• Energy conservation and the application of solar energy in FGD;
• Fuel preconditioning of for sulfur removal before combustion;
• Application of low-cost sorbent materials; and
• Sludge volume reduction and/or new methods for its recycling.

Dr. Farida El-Dars
Dr. Jin Shang
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• technical advances in FGD
• fuel pretreatment
• waste minimization
• design improvement
• waste recycling