Every process is different, so make sure to consider all of your process variables when looking for an oxidizer.
What are you to do? You need to specify and purchase a thermal or catalytic oxidizer to control the emissions from your process, and you do not know where to start. While this can seem to be a daunting task, you have all of the information necessary to ensure a proper selection: There is no one who knows your process and plant better than you do.
By collecting and organizing the information required in each of the following 10 tips, you will clearly define your requirements, expectations and specifications. This will help ensure that the correct oxidizer is selected for the process and that the installation and operation exceed your expectations.
Tip 1: Consider Regulatory Requirements
Understanding the regulatory and permit requirements is the first step. This entails more than just knowing the oxidizer’s destruction efficiency. In addition to that value (destruction efficiency or outlet concentration), the following additional questions should be addressed:
When is compliance required?
What downtime for maintenance or emergencies is allowed in the permit?
Are there any backup requirements?
Tip 2: Think about Location
Where the plant is located can affect the oxidizer selection. Some of the location issues that should be specified are:
How much space is available in the area where the equipment will be located?
Is the equipment to be installed inside or outside
What is the elevation?
Are there any special weather or environmental considerations?
What are the site conditions?
What is access to the site like?
Tip 3: Identify Pollutants
While the process exhaust volume has a significant impact on the oxidizer cost, the pollutants and other constituents in the exhaust also can impact the capital and operating costs. For that reason, any pollutants and other constituents should be identified.
What are the pollutants in the process exhaust? They may include volatile organic compounds (VOCs), hazardous air pollutants (HAPs) and hydrocarbons. In addition, particulate matter (PM), water (H2O), oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen and nitrogen-bearing compounds, silicon and silicon-bearing compounds, halogenated compounds, sulfur compounds and any other specific compounds should be identified. The concentration, or loading, of each should be identified for all operating conditions. It is important to identify all components because their presence can impact materials of construction or require ancillary equipment such as acid scrubbers, wet electrostatic precipitators (WESPs), dry particulate dust collectors or other means of particulate removal.
Tip 4: Describe the Process
It is important to clearly define the process and how it operates in your specification. The following questions should be addressed:
What is the process?
Is it cyclical, batch or continuous?
Your process is unique; therefore, any additional information that clearly defines the operation should be detailed.
Tip 5: Calculate the Volume
The process exhaust volume has the greatest impact on the oxidizer’s capital and operating costs: The greater the volume to be treated, the higher the cost. Therefore, it is important to accurately identify the volume in the specification in pounds per hour (lb/hr) or actual or standard cubic feet per minute (acfm or scfm) for different operating conditions. The temperature of the exhaust also should be identified for each flow condition.
Tip 6: Define the Operating Cycle
It is critical that the operating cycle of the process be clearly defined. Process cycling that might generate a peak volume or peak contaminant loading affects the size of the equipment. However, this is not the only limiting factor. For instance, there are cases where the pollutant concentrations or loading -- even at process exhaust flow rates less than the maximum -- may dictate that certain oxidizer components be larger in size or constructed with premium materials due to the temperatures that will be generated.
Tip 7: Add in Utilities and Utility Costs
Often overlooked, it is important to specify all potential utilities and utility costs that will affect the operating cost of the oxidizer. These include:
Fuel, including type, pressure and cost.
Electricity, including volts, phase, cycles and cost.
Steam, including pressure and cost.
Compressed air, including pressure, quantity and cost.
Tip 8: Think about Heat Recovery
Whether or not there is a need -- or even the potential -- for secondary heat recovery, be sure not to overlook this important aspect of specifying your new thermal oxidizer. Heat recovery systems can provide auxiliary heat for the process or for plant heating or cooling. The auxiliary heating can be performed in many ways, including:
Direct heating using the oxidizer exhaust.
Indirect heating using an air-to-air heat exchanger.
Indirect heating using an air-to-liquid heat exchanger (using hot water or oil as the heat transfer medium).
Generating steam with a waste heat boiler.
Providing cooling using an adsorption chiller.
It is important to identify how much auxiliary heating can be used and whether it is a full-time load or only required during a heating season. While some processes may not have enough waste heat that can be recovered for auxiliary heating, for others, an auxiliary system may have a short economic payback period.
Tip 9: Set Equipment Limits
Now that the process and operating conditions have been defined, you must define what you expect the oxidizer supplier to provide and what the battery limits are.
Of course, the first question that must be answered is: What type of oxidizer will be best for your application? Often times, there are different oxidizers that will fit the application, and the full evaluation of the items identified in the first eight tips will help narrow the possible choices.
It is recommended that you meet with potential suppliers and obtain conceptual proposals to aid in your determination of the best oxidizer for your application. Remember that each plant and process must be individually evaluated. While helpful to know, the types of oxidizers selected for similar plants and processes should be used as a reference only.
Tip 10: Write the Specifications
Finally, it is time to write the equipment specifications. The specifications should include all plant/corporate requirements for the purchase of equipment or services. The specification can be written in several ways:
As a design specification, where everything about the equipment is detailed.
As a performance specification, where the performance is detailed. How the equipment meets the specifications is determined by the supplier.
As a combination of the two methods. Specifications that combine the aspects of both design and performance specifications ensure that the equipment ultimately purchased meets your desired performance.
When writing the specifications, the scope of supply for both the supplier and the purchaser should be defined clearly.
Now that you have spent the time and effort to complete the specifications, it is time to solicit oxidizer proposals. Identifying vendors with the ability to supply any type of oxidizer may avoid biases toward any specific type. Enough time should be allowed for vendors to prepare their proposals.
Remember that although you have developed a clear and concise process and equipment specification, it will take some time to prepare a detailed oxidizer proposal. With planning and preparation, however, the end result will be an oxidizer that exceeds your operational and performance requirements.
While these tips are for new equipment, many of these same items should be addressed if you have a thermal or catalytic oxidizer that needs to be upgraded, expanded for additional capacity, or modified in any way.
This article originally was published with the title "10 Tips: Specifying a Thermal or Catalytic Oxidizer" in the September 2009 issue of Process Heating.
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