OCR Text |
Show ...... a....t. , . > S (.) •c • ~ (; ~ 100 It " I 50 - I (1) (2) Ref. cat SI resistant cat 0 I I I 0 5 10 15 (SI g/l - cat) Slicon Accumulation vs. Toluene Conversion Condtlort S . V. = 20.000 hr-1 Concentration (Toluene) = 1000 ppm wI Air Balance Figure 5 - Poison-resistant Formulation Masking Often systems are reviewed for viability in cleaning VOC streams containing combustible particulates. When a system is evaluated having a significant quantity of combustible particulate, another process addition is provided. This is done to avoid the potential for masking the catalyst by plugging the high surface area alumina with particulate. Systems now have been successfully designed utilizing an innovative concept of particulate combustion prior to introduction to the catalyst bed. The system, shown conceptually in Figure 6, consists of a ceramic monolith bed of minimal thickness placed close to the preheat burner. The burner continuously fIring the auxiliary fuel, heats the ceramic screen to a temperature at which the combustible particulate is able to auto-ignite. This screen provides both a filter element and a temporary place for the pre-combustion of these contaminants. The screen system has proven to be an effective measure to enhance the catalyst life of units operating in this service. Masking may be the result of non-combustible particulate in the waste stream or a unit that has not been designed with any particulate consideration. In this event, the particulate, while acting as a masking agent, is fairly inert and the catalyst can be readily regenerated by blowing off the dust with a high velocity gas stream. This gas stream is usually clean compressed air; however, other times there may be considerations used to select nitrogen or another gas stream. 6 |