Question
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What are the latest advances in FCC SOx reduction, and what levels can be achieved?
Mar-2021
Answers
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Hernando Salgado, BASF Catalysts, hernando.salgado@basf.com
There are several methods to effectively reduce SOx emissions in an FCC unit, such as feed hydrotreatment, wet gas scrubbers, and SOx reduction additives. While the first two solutions can reduce the emission by 70-95%, they also involve considerable investments and operating costs. On the other hand, the use of a SOx reduction additive, such as BASF EnviroSOx, is a cost-effective solution that can be applied when a moderate reduction is required.
EnviroSOx can capture SOx by using a MgO based material with enhanced retention, in order to maintain its SOx capturing abilities longer than other SOx reduction additives. In addition, a Ce based compound is added to promote oxidation from SO2 to SO3, together with V2O5 which assists to achieve a full regeneration of the MgO. As can be implied, the combustion mode of the unit is one of the factors affecting the additive performance; since nearly 90% of SOx is SO2 and a certain O2 excess is needed for it to be converted to SO3, partial burn units are more challenging.
Specifically, EnviroSOx has been successfully applied in a broad range of uncontrolled SOx concentrations in the flue gas up to 7000 mg/Nm3, either in full or partial burn units. One of the main parameters to monitor the additive performance is the pickup factor (PUF), defined as the amount of SOx captured per mass of additive, expressed in kg-SOx per kg-additive. In the case of EnviroSOx, the PUF can vary from 15 to 80, achieving SOx reduction rates up to 90%, with an average of 40-75%, depending on the specific process conditions and additive dosage in every FCC unit. Some examples of using EnviroSOx in FCC units are presented in Table 1.
Mar-2021
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