At CPI we have a great team of knowledgeable, dedicated professionals that bring years of experience to the work that we do in providing air pollution control solutions to our customers. As part of our ongoing look at maintaining your Catalytic Oxidizer (CatOx), today we're looking at catalyst maintenance.
How Does Annual Catalyst Testing Keep You EPA Compliant?
The Catalyst is an essential component of a CatOx, so ensuring that it is functioning properly is crucial for keeping your emissions within EPA standards. Catalyst activity does not typically drop off dramatically under normal circumstances. With annual catalyst testing, the life of your catalyst can be predicted with good accuracy. In some instances, tests will find a noticeable decrease in temperature rise, which can be directly proportional to a drop in the destruction efficiency. From experience, this often occurs between 30,000 and 50,000 operating hours, depending on a variety of factors.
The life of a catalyst is dependent on the type of volatile organic compounds (VOCs), the amount and type of inorganic masking agents present, the number of times the catalyst has been cleaned, and the oxidizer's operating temperature. Typical catalyst masking agents are silicon, phosphorous, and base metals such as iron, lead, nickel, chrome, tin, and titanium.
The performance of the catalyst depends on how well the catalyst is maintained during its operational life. Let's look at how you can keep your catalyst properly maintained:
Field maintenance of VOC catalyst is limited to high temperature de-carbonization and dust removal. If the operator determines that the temperature rise has diminished from when the catalyst was fresh, it is possible for the operator to perform a couple of operations to try to reclaim some of the catalyst performance.
Occasionally, condensable organic matter and carbon will accumulate on the surface of the catalyst. These materials can mask or block catalytic activity. It is possible to carefully remove these materials thermally via a "burn-out." A burn-out should be performed while the process is not running and sending VOC laden air to the oxidizer. Fresh air should be allowed to flow into the oxidizer at maximum flow. The oxidizer temperature can slowly be increased to approximately 950 - 1000°F entering the catalyst. At this temperature, with no VOCs present, the catalyst will burn off accumulated unburned VOCs and organic particulate matter.
Note: Extreme care must be taken not to exceed these temperature limitations. An adequate period of time for the burn-out should be between 2-3 hours. On occasion, some smoking could occur as a result of rapid burning of accumulated carbon.
If the pressure drop across the catalyst has been increasing, then it will need to have the accumulated dust removed. This procedure should be performed after the high temperature burn. The catalyst should be removed manually from the oxidizer and blown out using an air lance at not more than 80 psi. Air lancing with the catalyst in situ can be done with two people. The second person should stand on the opposite side of the catalyst bed and vacuum the dust which is being blown through the catalyst cells.
If either or both of the above procedures do not satisfactorily improve the catalyst performance, then it may need chemical rejuvenation. The effectiveness of chemical cleaning can be determined by CPI with activity testing before and after cleaning.
Testing Your Catalyst
As you have read above, catalyst testing plays an important role in staying EPA compliant. Below are instructions on how to pull a sample of bead catalyst (ceramic beads or spheres, usually contained in a catalyst tray):
- Shut down the oxidizer and wait for the internal temperature to fall below 100°F (reference your oxidizer operating manual for the proper shutdown procedure).
- Open the access door to the catalyst inlet bed (the door closest to the visual site ports).
- Enter the catalyst chamber, while following any applicable plant safety procedures for confined space entry.
- Select a tray near the center of the oxidizer (i.e. the middle tray if there is an odd number of trays or either of the two middle trays if there are an even number of trays; do not select the top or bottom tray).
- Remove the clevis and cotter pins from the front cover piece.
- Remove the front and top covers.
- If guard bed is included (white catalyst), obtain a sample of the guard bed. Take the sample from near the center of the tray. Carefully scoop a quantity of at least 200 cubic centimeters (CC) into an appropriate sample container. Note that this layer of guard bed is typically only 2” deep, with a protective mesh underneath, so you will not be able to scoop very deep.
- To obtain a sample of the catalyst, you will need to access it underneath the guard bed layer and protective mesh. After the the covers have been removed (see step 6 above), you should be able to push the guard bed beads towards the back of the tray. Lift the protective mesh at the front edge of the tray, being careful not to mix the guard bed beads with the catalyst beads. Scoop a quantity of at least 200 CCs of catalyst into an appropriate container from the center of the tray. Note that there is a second layer of protective mesh with another layer of catalyst underneath, so you will not be able to scoop to the bottom of the tray. You only need to sample from this layer of catalyst, not the bottom-most layer.
- Smooth the catalyst remaining in the tray where the sample was taken from.
- Replace the protective mesh between the guard bed and catalyst.
- Smooth the guard bed evenly across the tray.
- Replace the covers, clevis pins, and cotter pins.
- Exit the oxidizer and replace the access doors.
- Put the oxidizer back into service.
Once you have obtained the catalyst sample, you can visually inspect it to determine its level of carbon buildup or dust accumulation. Your sample can also be sent in to our laboratory for further testing.
Contact Jeff Nasticky to schedule your catalyst test -
Our engineering and service team have compiled an ebook that we hope can help operators of catalytic oxidizers and catalyst reactors achieve optimum performance.
Read our ebook Catalytic Oxidizer Design and Operations Basics for information on:
- Catalyst Inhibitors
- Analytical Services
- Removal and Installation Guidelines
If you're working on an air pollution control project and have some questions, please contact us: