Emission Control Technology
Spray Dryer Absorber (SDA)
Spray Dryer Absorbers facilitate the removal of acidic pollutants, heavy metals, and dust from flue- and off-gases at fossil-fuelled power plants, waste incinerators and industrial installations.
The Spray Drying Absorption process – a semi-dry flue gas desulphurization and cleaning process – facilitates a reaction efficiently transforming gaseous pollutants such as e.g. SO2, SO3, HCl, Hg, and dioxins into a slaked lime Ca(OH)2 absorbent to form a stable and dry powdery product that is easy to store and transport.
Every Spray Drying Absorption process is tailored to meet the client’s requirements as well as applicable environmental legislation. The absorbers boast well-proven system features such as e.g. peak-control and activated-carbon injection which have been designed for the purposes of ensuring low mercury and dioxin emission.
Benefits
- High acid-gas removal efficiencies
- Low capital, operating and maintenance costs
- Low power and water consumption – operates on low-quality water
- High plant availability
Spray Drying Absorption process
Process for Power plant and Sinter plant applications
The essential process stages are:
- Absorbent preparation and dosing
- Removal of Sox (acid gases)
- Solids recirculation and product discharge
Hot, untreated flue gas is introduced into the Spray Dryer Absorber via a flue gas disperser and subsequently comes into contact with a highly reactive absorbent that will be atomized by a Rotary Atomizer.
An efficient contact between flue gas and absorbent allows for rapid mass transfer of acidic components from the flue gas into the alkaline absorbent. The absorbent neutralizes the absorbed acid (SO2 + Ca(OH)2 -> CaSO3/CaSO4 + H2O). While this reaction takes place, the water is evaporated, thus forming a dry powder. A fraction of the dry powder will be deposited at the bottom of the absorber chamber and discharged from here, whereas the main part is carried to the downstream dust collector while the cooled flue gas leaves the chamber. The flue gas – now clean – passes from the dust collector to the stack without re-heating.
Key Components
The Spray Dryer Absorber – the Rotary Atomizer, the Gas Disperser and the Absorber Chamber – is the heart of the Spray Drying Absorption process.
Spray Drying Absorption - the unique use of the spray drying technology for acid-gas absorption - was originally invented by GEA in the 1970s.
Ever since, it has been subject to continuous further development and optimized to meet changing conditions and requirements. Hence, the process stands as an efficient, versatile and thoroughly tested technology.
Rotary Atomizer wheel
This wheel is the key element in the SDA and atomizes the absorbent liquid into flue gas. The fast-rotating wheel breaks the liquid into an atomized mist of exceptionally small droplets with immense surface areas.
Gas Dispersers
Gas dispersers serve to optimize the distribution of flue gas inside the absorber chamber, facilitating the best contact between the flue gas and the atomized droplets of absorbent feed.
Spray Dryer Absorber chamber
The flue gas enters the SDA chamber, a cylindrical steel construction, via the gas disperser and leaves through an outlet duct at the coned bottom. The Rotary Atomizer installed centrally allows the gas to mix with the feed.
Applications and references
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Power plants |
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Small boilers |
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Sinter plants |
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Smelter plants |
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Pelletizers |
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Coking plants |
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Worldwide, more than 700 Spray Drying Absorption plants are installed at power stations, steel plants, waste incinerator plants, and at plants burning hazardous waste. They all share one common trait: They are operated in accordance with or above required performance stipulations as laid down by local authorities. Even today, the very first plants, installed in the 1980’s, are still operating satisfactorily and successfully.
Industries that profit from a SDA system
Explore how GEA’s SDA systems can be tailor-designed to meet the rigorous demand of diverse industrial environments, offering robust performance, flexibility and comprehensive support to ensure energy efficiency, optimal operation and compliance with environmental standards.
Power plant applications
The Spray Drying Absorption process is a versatile way of cleaning flue gases by the removal of acid gases and particulates generated by fossil-fuel burning, mainly coal. Because of the presence of large volumes of flue gasses, power plant installations frequently have more than one Spray Dryer Absorber module. A compound-gas disperser ensures an optimum gas flow, even at very large volumes. The considerable plant size and gas volumes normally favor recycling of the end product, allowing operation at low outlet temperatures, no more than 10 - 15° C above adiabatic saturation temperature.
The end product from Spray Drying Absorption consists of the reaction products, excess absorbent and fly ash. The SO2/HCl ratio of the inlet gas is high, thus allowing for operation close to the adiabatic saturation temperature and minimizing the content of lime in the end product. A Spray Drying Absorption system can achieve very high desulphurization rates, practically only limited by the accepted content of excess lime in the end product.
Sinter plant applications
Spray Drying Absorption is the ideal solution for removing dust and acid-gas exhaust from sinter plants.
Spray Drying Absorption installations for sinter plants combine features from power- and waste incineration plants.
Flue gas volumes are normally high; and, hence, necessitate the installation of large absorber modules. But, frequently, acid contents will be relatively low, thus allowing for the use of single pass systems.
Variations in gas quality may occur relatively fast, and therefore the control system must be designed to act accordingly. To a large extent, absorbent used for sinter plant applications will be purchased and stored as CaO for subsequent on-site slaking. The Rotary Atomizers applied in sinter plants are generally F-360, F-800 and F-1000, equipped with stainless steel wheels and central parts.
Process for Power plant and Sinter plant applications
Waste to Energy applications
Spray drying Absorption is a means to meet the strict emission regulations applying to waste-incineration plants.
Waste incinerator applications are generally characterized by relatively low gas amounts; and, hence, the absorber is constructed with only a roof gas disperser. The smaller plant size and the composition of acid content typically favor single-pass designs. The Rotary Atomizers employed in waste incinerator plants, SDAs, are normally type F-100, equipped with wheels in Hastelloy.
The high HCl content in the gas gives rise to a considerably higher inlet gas temperature than seen in power plant applications. Consequently, the end products will show different behaviors. Further, the moisture and O2 content of the waste gas is higher. The drying properties of the absorber, high chloride content in the end product, single pass mode, etc., call for a design with higher retention time in the absorber chamber, and therefore the plants are operated at high outlet temperatures.
Process for Waste to Energy applications
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