Add or replace?
The key to managing catalysts effectively is to determine an optimum catalyst replacement/addition plan (that is, when a catalyst should be replaced or an additional layer added). As discussed, the key factors of this assessment include performance audits that analyze the remaining potential of the catalyst. The remaining life of the field catalyst, analyzed in conjunction with the operating history and projected use of the SCR, outage schedule and economic/financial factors, are used to decide what catalyst action should take place.
In most cases, SCR catalyst reactors were built with at least one spare layer. Utilization of this layer generally results in the best economic option for utilities due to the significant life benefit provided vs. removing and regenerating a layer. Therefore, for most utilities, catalyst additions will be the first action, followed by replacements or rejuvenation. Because catalyst layers will deactivate at different rates depending upon the fuel fired, the information dictating which layer should be replaced will be generated from the performance audit, which may also be potentially applied to other fleet units considered at the time.
An important step to include in this decision process is associated with catalyst advancements available at the time of need. For example, in units that have either a large pitch or a short catalyst length, there is substantial opportunity to improve the performance potential of the unit. This may be important when considering issues such as the value of eliminating the cost associated with an SCR catalyst action during a planned outage, generating NOx credits, and—in some cases—meeting a mercury emissions-reduction goal.
Transitioning to an alternate product can be done in a staged and qualified manner to minimize any risk of a wholesale change in the catalyst. Alternately, this method may be used to reduce the cost of the purchased catalyst by taking advantage of the performance benefit through reduced volume. In either case, catalyst advancements should be an integral part of the management planning process. In some cases, they can provide more than a 50% performance enhancement or cost reduction, compared to installing a new layer of the original catalyst.
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