February 15, 2006

Long-term catalyst health care

Scot Pritchard, Cormetech Inc.

Rejuvenating a catalyst

Cleaning can be a highly effective catalyst performance recovery method in plants where excessive accumulation of particulate matter is affecting emissions performance and increasing draft loss. Cleaning refers to removal of physical restrictions due to buildup of LPA or popcorn ash, and/or flyash that blocks flue gas access to the catalyst surface. Cleaning methods can be dry or make use of an aqueous solution. Cleaning may be done in situ, on-site, or off-site.

The dry method of cleaning typically involves a combination of vacuuming and air lancing to remove the ash from the reactor; in gas applications, it also may include removal of insulation debris and/or rust scale. This process is typically very effective where the modules have flyash buildup but no LPA in the catalyst. This can be performed in situ or off-site, depending on site logistics and outage considerations (Figure 6).

6. Dry cleaner. Dry cleaning using vacuuming/air lancing can reduce catalyst fouling due to buildup of large-particle ash and ash fines. The example below shows reduction from 30% to 50% on average. Courtesy: Cormetech Inc.

Wet cleaning of severe ash buildup on a catalyst cleaning is referred to as washing, regeneration, or rejuvenation (Figure 7), depending upon the process and aqueous solution used. This is a more elaborate cleaning process that removes most of the chemical buildup on the catalyst surface. The process generally restores the catalyst activity lost to both gross and fine physical blockage. In addition, the process can be used to restore all or a portion of the catalytic activity lost due to chemical poisons.

a. Removal of ash

b. Vacuuming

c. Washing using a cleansing solution

d. Bubbling and aeration under pressure

 7. Rejuvenation. These images depict some of the stages in SCR cleaning using the rejuvenation process.


Generally, the regeneration process consists of the following steps:

1 Baseline testing of the catalyst to assess performance recovery.

2 Blowing and vacuuming ash off the catalyst.

3 Adding ultrasonic energy, bubbling air in the solution and/or physically moving the module to remove any remaining ash.

4 Washing the catalyst module using a cleansing solution. This may need to be done multiple times, with different solutions, in accordance with the system vendor's recommendations.

5 Drying each catalyst module using forced hot air.

6 Testing the catalyst elements to verify that the cleaning has met the established goals.

Regeneration/cleaning must be considered at every plant where the condition of the catalyst condition and its remaining service life dictate it. If it is determined to be economically advantageous to the plant, catalyst cleaning can extend the active life span of a catalyst and be an essential part of a catalyst management program for a plant. In all cases, the process should be prequalified on samples prior to implementation of the full-scale process. Items for consideration include the level of activity recovery (physical or chemical), the impacts on SO₂ conversion and mercury oxidation, cost, schedule, and any applicable warranty conditions.

—Scot Pritchard is VP, Sales and Marketing at Cormetech Inc. He can be reached at 919-595-8708 or PritchardSG@Cormetech.com.