OCR Text |
Show 1.0 INTRODUCTION (con't) 1.3 Special Features of Shell Denox Technology Here we enumerate some special features in which Shell denox technology distinguishes itself from competing technologies. • The low temperature activity of Shell catalyst makes it possible to retrofit an existing flue gas heat recovery system with a Shell denox unit without having to break into the economizer tube bundles in search of a suitable temperature level. This may constitute a significant cost saving, both in terms of capital expenditure and downtime. • The low-T feature may also have safety/reliability advantages. For example, in a gasoil cracker or a refinery furnace, a tube burst could lead to the release of flammable hydrocarbons. It could be that the ignition of these HCs is catalyzed by the denox catalyst. Such ignition could lead to sintering and consequent irreversible damage to the catalyst. The lower the operating temperature, the more likely that ignition will not occur. • The quick unloading option of the LFR may represent a significant advantage in plants where minimization of downtime is a prime concern. A complete catalyst change of an LFR system could probably be effected within hours or even less (depending on the size of the system), whereas the same operation for a conventional modular system probably costs a few days. • The high strength of silica based catalyst is advantageous in systems where very rapid temperature rises are to be expected during system start-up (e.g., gas turbines). It is well known that honeycombs and plate catalysts experience problems due to thermal stress (cracks, detachment of washcoats from plates). To overcome these problems, the catalyst must be equipped with some preheat device. No such precautions are necessary with Shell silica catalyst. • At higher temperatures (say > 5000 F), LFR designs generally have very high space velocities, resulting in small, compact and light-weight reactor designs. The latter feature (weight) may be of prime importance in retrofit designs where extra civil work on existing installations is obviously not welcomed. 3 |