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Combined heat and power plants that burn sulfur-containing fossil fuels, like coal and fuel oil, and many calcining plants, chemical and petrochemical production facilities, such as fluid catalytic cracking plants (FCC), often produce large quantities of sulfur-oxide-containing flue gases.
In addition to this, incinerators, hazardous waste incineration plants in the chemical industry and sewage sludge incinerators are sometimes significant sources of SOx emissions too.
Once released into the atmosphere, sulfur oxides react with moisture in the atmosphere to form sulfurous acids, and sulfuric acid is a component of acid rain. Still one of the main causes of soil and water acidification, as well as corrosion damage to buildings and other structures worldwide.
Wet flue gas desulfurization plants from Steuler Equipment Engineering work using the limestone/gypsum process, as has been standard practice in large-scale power stations for decades. It is probably the most effective wet scrubbing process for reducing sulfur oxides there is at the present time. It features a particularly attractive combination of low operating costs, high DeSOx removal capacity and efficiency.
This especially sustainable process uses naturally occurring limestone and generates so-called FGD gypsum, a free-flowing reusable material that is becoming increasingly sought-after in the building materials industry due to its high purity and quality (euro gypsum).
The use of inexpensive consumables combined with a marketable end product in the form of gypsum explains the large operating cost benefit of the wet FGD process compared to the significantly less effective dry flue gas desulfurization process, which generally uses much more expensive absorption media, like hydrated lime or sodium hydrogen carbonate, and whose waste products have to be disposed of underground.
The modular plant and process engineering technology developed by Steuler allows the operators of small to medium-sized plants to enjoy the benefits of FGD technology that is normally reserved for large-scale power plants.
Steuler flue gas desulfurization units based on the limestone/gypsum process are typically used in the following industries:
Focusing our wet FGDs on small to medium-sized plants, i.e. with flue gas flow rates of between around 20,000 Nm³/h and 600,000 Nm³/h, allows the construction of individual component assemblies to be standardized. As a result, the operator can take advantage of industry-proven, high-availability equipment and plant systems for a comparatively low price. Since the interfaces between the individual component assemblies are harmonized, it's possible for sub-systems that are less functionally relevant, such as tank and bulk storage systems, buildings, steelwork and sub-assemblies to be provided by the customer in consultation with our project planning team.
Although limestone/gypsum FGDs are classified as so-called wet scrubbing processes, most of the FGD units constructed by Steuler thus far generate no or just a few hundred liters of wastewater per hour. Surprisingly, water consumption is only slightly higher than that of a comparable dry system based on hydrated lime.
The acidic gaseous sulfur oxides are absorbed by the scrubbing liquid, a suspension of ground limestone, gypsum crystals and water, and react with the added absorbers to form the insoluble, reusable end product gypsum, i.e. calcium sulfate of high purity, which is then extracted from the process by filtration.
Depending on availability at the site, Steuler can configure wet FGDs to operate using inexpensive calcium compounds like CaCO3, CaO or Ca(OH)2 or alternatively ZnO, Mg(OH)2 or even sea water. The respective product formed can usually be either fed back into the primary process or sold as a raw material. The underground disposal costs normally incurred with dry FGD processes are completely eliminated.
Steuler Equipment Engineering offers an additional flue gas desulphurization process for flue gas streams with a lower sulfur oxide load in the form of so-called chemical scrubbers, typically based on a neutralization reaction using caustic solutions (e.g. NaOH, NaHCO3, KOH etc.).
In order to meet the particular requirements of our industry partners with respect to price, durability, operating simplicity and availability, Steuler Equipment Engineering has developed robust and cost-effective scrubber tower designs tailored to the respective flue gas volumes.
Steuler can supply prefabricated and ready-to-install FGD exhaust gas scrubbers with diameters of up to 4 meters, which corresponds to a flue gas volume of around 100,000 Nm³/h. The preferred materials are thermoplastic polypropylene or glass-fiber reinforced plastic (GRP). We can also construct absorbers with larger diameters that are too big to transport using the innovative reinforced concrete/Bekaplast construction method developed by Steuler, whereby the inside of the scrubbing tower is permanently protected against corrosion by means of mechanically anchored protective plates.
A construction method that has so far proven to be eminently suitable for many different applications and extremely competitive too, especially in developing countries.