Air pollution control equipment is not something that business owners address by saying, “Let’s do the right thing for the environment and install an oxidizer!” In fact, the scenario is more likely to be “We need to increase productivity (always a good thing!), but that will put us over our annual emissions limits. Do we know what we will need? Where do we start? Who can help us?”There are many factors that impact whether air pollution control equipment is required. How do you know which control device is correct for your application? As mentioned in Part 1 of our blog series “How Long Does it Take to Build an Oxidizer?”, part of the client buying process is a technology review. It is important for the plant's engineering staff to discuss the application data with potential suppliers. This will help determine options for the customer to meet or exceed their environmental goals or outcomes. The air pollution control equipment supplier will then be able to direct the customer to the appropriate Best Available Control Technology (BACT) or Maximum Available Control Technology (MACT).
Typical application data that should be discussed includes:
- Process Type
- Process Exhaust Rate (Air Flow)
- Exhaust Temperature
- VOC type
- VOC loading (lbs/hr.)
- Particulate (Y/N)
- Particulate Size
Let's take a closer look at some of this data and how it affects the decision of which air pollution control technology to use:
Air Flow: This is measured in Standard Cubic Feet per Minute (SCFM), with the volumetric flow rate of the process gas corrected to "standardized" conditions of temperature and pressure. This represents a fixed number of moles of gas regardless of composition and actual flow conditions.
Note: air flow can also be measured as Nm3/h (Normal Meters Cubed per Hour).
(Process) Temperature: This can range from ambient air temperature (the overall temperature of the outdoor air that surrounds us) to very high process temperatures greater than 500° F.
VOC Loadings: The amount of volatile organic compounds (VOCs) will need to be identified in both the worst case scenario (highest) concentration, and normal operation scenarios. VOC concentrations can play a huge role in the operating expense (OpEx), such as electrical and natural gas usage, consumable parts, and maintenance, of the equipment. For example, the operating cost for a thermal oxidizer might be higher than a regenerative thermal oxidizer due to the natural gas usage required. However, it might be possible to recuperate some of the cost by installing a heat recovery system as well. The capital expense (CapEx), large equipment purchases, may show a quick payback by lowering the OpEx.
VOC concentration is also evaluated for safe operation of the system. Most of the time the VOC concentration is converted to a percentage of the Lower Flammable Limit (LFL) in the exhaust stream to be treated. The LFL is the lowest concentration (percentage) of a gas or vapor in air capable of producing a flash of fire in presence of an ignition source (arc, flame, heat).
Required VOC Destruction Rate Efficiency (DRE): This number is typically >95% and may be as high as >99%.
Here are some additional questions that we ask to determine the best air pollution control technology for a customer's process:
Does your process contain contaminants?
Silicone, for example, can build up on heat exchanger tubes, burners, and fans, and it can create maintenance nightmares if the wrong technology is chosen. Silicone will also mask the catalyst – which makes a catalytic oxidizer a poor technology choice (at times) for an application that can contain silicone.
Does your process contain particulates?
Processes such as tape manufacturing and web coating can contain particulates, like silicone, that can build up throughout the system, causing maintenance headaches and decreased oxidizer performance. In some cases, particulates can be eliminated by placing a filter in front of the oxidizer system, and this type of filter can be used regardless of the technology chosen. However, in some instances, the particulate is actually formed inside the combustion chamber of the oxidizer, which adds several more layers of consideration when selecting the correct control device.
Is the exhaust stream corrosive?
Does the air stream anything acidic which can be corrosive to the areas of the oxidizer that it comes in contact with? Special care needs to be taken into consideration when choosing construction materials and special coatings to prevent material failures.
How much space have you allotted for your new air pollution control equipment?
If you are incorporating a large piece of equipment at the end of a process line in a new facility, space may not be an issue. But if you are trying to maximize every square inch of the building you have been at for 40 years, you may face some interesting challenges, and space consideration may be an influence on the decision of which technology would best suite your needs.
At Catalytic Products International, we work to make sure that our customers have the best solutions to their air pollution remediation needs and that they have the knowledge to continue to meet these needs as they grow and change. For more examples of how our expertise helps our clients find success, please read our Customer Testimonials.