Spray dryer absorbers in USA
The SDA process is a versatile way of cleaning off-gases or flue gases from many different sources, e.g. power plants, waste incinerators, sinter plants, and hazardous waste incinerators. The SDA plant will be designed to adapt the applicable specific conditions and requirements at the location in question, so each individual SDA plant may differ from the other. Learn more about spray drying absorption.
Power plant applications are normally characterized by one or more absorber modules using compound gas dispersers for optimum flow distribution into an absorber chamber of large inlet gas flow rates generated by the burning of fossil fuels, mainly coal.
The considerable plant size and gas volumes normally favor recycling of the end-product, allowing operation at low outlet temperature, just 10 - 15° C above the adiabatic saturation temperature.
All flowsheets are available for download in the Animation Download area.
The end-product from an SDA plant naturally consists of the reaction products plus excess absorbent and any fly ash. The ratio of SO2/HCl in the inlet gas is high, which allows for operation close to the adiabatic saturation temperature, minimizing the content of lime in the end-product. An SDA system operated at the described conditions can achieve very high desulphurisation rates, practically only limited by the accepted content of excess lime in the end-product.
The rotary atomizers used for power plants SDA’s are normally the F-350 and F-800, equipped with stainless steel wheels and central parts.
The normal changes in operation of the upstream flue gas generator are generally so smooth, both when it comes to gas amount and composition, that control of outlet temperature and emissions are achieved by simply mixing the feed streams of absorbent and recycle slurry (or water) in the above head tank. To a large extent, the absorbent used for power plant applications is purchased and stored as CaO and then slaked on site.
As shown in the animation, the hot untreated flue gas is introduced into the absorber module via gas dispersers for optimum gas flow distribution and contact with the absorbent sprayed by the rotary atomizer. The efficient contact between the gas and atomized absorbent slurry allows for rapid mass transfer of acidic components from the gas phase into the liquid phase.
The alkaline absorbent neutralizes the absorbed acid and the desired reaction product is formed while water is evaporated simultaneously. A fraction of the dried end-product drops to the bottom of the absorber chamber and is discharged, while the main part is taken to the downstream dust collector with the cooled flue gas and removed from the gas. The clean gas passes from the dust collector to the stack without re-heating.
Following the absorption of acidic components, the chemical reaction, and the final drying, the powdery end-product is separated from the gas phase and transported to an end-product storage facility or re-used in the SDA process for the improved utilization of excess absorbent. Whether or not to design the SDA plant as a single pass system or to include a recycle system depends on the inlet gas quality and emission requirements.