These air pollution control systems destroy harmful VOCs and air toxic pollutants contained in process exhaust fumes at elevated temperatures. The methods used (catalytic or thermal oxidation) assure complete VOC/HAP destruction. Today’s energy efficient air pollution control systems utilize high-efficiency heat exchangers to preheat incoming exhaust fumes, thus further reducing operating costs.
A Specification Checklist
Once a decision has been reached to purchase an air pollution control system, the company should select several experienced vendors and provide them with specific design specifications and details that can be used as a basis for preparing formal proposals.
When requesting a proposal from a system manufacturer, it’s best if the following information is provided:
• Describe the type of production process emitting the air pollutant to be controlled. If possible, include a rough sketch of the building floor plan showing the location of all pertinent production equipment.
• Provide the geographical location (and elevation level if known) where the system will be installed. Both the outdoor climate (surface finishes/types of dampers, etc.) and the elevation (fan sizing) could have an effect on system design.
• Estimate the number of hours per day that the system will be operated. The heat exchanger efficiency, chamber design, etc., could possibly change depending upon the operation hours required.
• List the total number of different emission points (exhaust stacks) that are to be controlled by the air pollution control system. A process control/bypass tee-damper may be required at each emission point. The system’s electrical control design will also change depending on the number of dampers to be controlled.
• List the exhaust rates and temperatures for each individual emission point. The exhaust rates are important for sizing the unit, but they are also used to size the ductwork and dampers. The temperature is used to calculate estimated operating costs and to determine the necessity for ductwork insulation.
• Describe the type of heat source used for any dryers/ovens that are to be controlled. If the heat sources for process dryers or ovens are gas-fired burners, National Fire Protection Association (NFPA) regulations will determine the method of purging and damper control. If the heat source is by steam or hot oil, process control/bypass tee-dampers might not be required at each stack.
• List the air pollutant types and quantity being emitted. In addition to affecting the choice of catalyst used in catalytic units, the solvent type and quantity will also affect the VOC destruction efficiencies, the heat exchanger efficiency, the internal materials of construction and the estimated operating costs.
• Determine the possible need for a permanent total enclosure (PTE). Based on the ability to demonstrate high capture efficiency, the use of PTE’s have become very popular in many industries and may be worth considering. Permitting a facility with a properly designed PTE will assure 100% capture of all air pollutants present within the production area. Depending upon the PTE design, it might or might not affect the overall sizing and technology choice of the air pollution control system.
• Provide the electrical voltage and available power cost. The voltage available determines the type of electronics that are used. The power cost is used to calculate the estimated operating costs.
• Provide the type, cost and line pressure of supplemental fuel available. The fuel type (natural gas, propane, etc.) and the line pressure are used to determine the burner and fuel train design. The fuel cost is used to calculate the estimated operating costs. Compressed air might be required, depending on the design of the air pollution control system.
• Describe the physical location of the air pollution control system installation. The actual location determines whether a concrete equipment pad or steel support structure is required. Also, if possible, provide specific site installation plans, such as duct run length, exhaust stack height and gas piping length required.
• Indicate the percentage of pollutant destruction efficiency required. The destruction efficiency percentage required will determine the amount of catalyst needed (in catalytic models), as well as the operating temperature and residence time in either technology.
• List any catalyst masking or poisoning agents that could potentially be present in the air stream. Compounds such as silicones, phosphorus, heavy metals, halogen, sulfur and any particulates could be of concern and should be identified. An air pollution control system can be designed to handle various levels of most compounds if the user can quantify them in advance.
• Plan ahead. When selecting or sizing an air pollution control system, the facility’s growth expectations for the next two to five years should be considered. It is typically less costly to install a system designed to handle additional capacity now rather than to install a second system in the future.
Unfortunately, it can be very difficult to understand the bona fide differences between one air pollution control system manufacturer’s offerings and another’s. When evaluating a system for purchase, there really isn’t any product testing that can be done for review, so purchasing decisions typically are made by relying on the vendor’s credibility and on the assembled design data. The more thorough and precise your company can be in providing operating and design criteria, the more likely your project will culminate with an air pollution control system that will meet your individual needs and provide many years of trouble-free service.