Rejuvenation vs. regeneration
In some cases, rejuvenating catalyst may be more cost-effective than regenerating it, especially if the catalyst life is fairly new or if its SCR system doesn't operate year-round. Rejuvenation is much more than cleaning pluggage and flyash from the catalyst. In addition to cleaning the catalyst, rejuvenation removes blinding layers and some poisons; this recovers some activity but adds none. Regeneration includes cleaning and rejuvenation, plus the addition of active ingredients to restore the catalyst to 100% or more of its original activity.
Onsite cleaning has been used in a number of instances where pluggage is the only concern. Depending on the amount of blinding and poisons present, it is usually better to go with deeper ultrasonic cleaning and exercise the option to reactivate the catalyst. Doing so eliminates onsite handling, the use of chemicals, and outage coordination activities—but it does incur transportation costs.
The comparative economics of the two options depend on the following:
- The plant's dispatch economics.
- How long the catalyst has been in service.
- The design margin and effectiveness of the SCR system.
- The costs of removing and replacing the catalyst.
- The impact on the catalyst of the fuels fired.
Even if the catalyst has not plugged precipitously and retains most of its activity, the costs of catalyst removal and reinstallation often make regeneration the more economical approach. Alternatively, in-situ cleaning may suffice to correct certain fouling conditions.
Catalyst management: Still a must
The most effective way to operate catalyst is via a thorough catalyst management program (see p. 26). There are a considerable number of options for optimal catalyst management: add a layer; replace a depleted layer with new or regenerated catalyst; or mix and match plate, corrugated, or honeycomb catalyst in the same reactor. All of these options will change with year-round SCR operation.
No matter which catalyst type is being used, there are many possibilities for minimizing costs associated with a fleet of SCR systems. Other considerations include trying to match the use of catalyst to scheduled outages—the intervals between which are getting longer. This alone may mean planning for catalyst replacement in multiple layers.
There are also possibilities for managing or avoiding catastrophic catalyst failure. Pooling spare catalyst within the fleet and even within the industry at a central location can provide a safe margin for avoiding long, unplanned, and economically devastating outages. This strategy can be accomplished without a large investment.
SCR-Tech has developed many programs that can evaluate nearly any catalyst management scenario. These programs can predict catalyst life, allow for the mixing and matching of different catalyst types, handle multiple fleet SCRs, and evaluate site-specific economics associated with each scenario. They also provide risk assessment associated with extending catalyst life, based on previous experience. These assessments are always backed by independently verified third-party catalyst testing.
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