Handling volatile organic compounds & odor control in animal feed manufacturing
You may have thought animals only eat plants, grass or some other food natural to their species. However, animals not only need protein and energy, they also need vitamins and minerals. Feeding livestock is a complicated task and the global feed additives market continues to be a growing industry.
Animal feed is a formulated mixture created by animal nutritionists to provide the animal with the necessary balanced nutrients for proper growth, development and maintenance. Feed is designed to compensate for nutrients and supplements that may be absent from an animal’s natural diet. Feed additives are supplements including vitamins, amino acids, fatty acids and minerals used in animal nutrition for purposes of improving the quality of feed and the quality of food from animal origin, or to improve the animals’ performance and health.
The basic manufacturing process begins as raw materials are conveyed from storage silos to reactors through weigh hoppers. From the reactors, product is routed to product coolers and is then conveyed through enclosed systems, where material is sorted, blended, and sent to the packaging areas. Odor, volatile organic compounds (VOCs)—including sulfur-based compounds—and ammonia, are released to the atmosphere during the production process.
Thermal oxidation is the most widely accepted air pollution control technology available to control the odor, VOC emissions and ammonia from the animal feed manufacturing process.
Oxidation of VOCs and other air pollutants works by oxidizing the air pollutants with oxygen and heat. In this environment the VOCs are converted to harmless inert byproducts such as carbon dioxide, water vapor and usable heat. These byproducts are released to the atmosphere or used within primary or secondary energy recovery techniques to further lower the operational costs.
One southern U.S. animal health and nutrition company entrusted Catalytic Products Intl. (CPI) to design, manufacture and install several control thermal oxidizer systems for the abatement of odors, VOCs and ammonia from its animal feed manufacturing process.
The oxidizers’ design addressed the following concerns:
- Accept air streams with a range of different flows and loadings from several product formulations.
- Eliminate particulate matter in the air streams. Although the production process equipment included a dust collector and various filter systems, additional particulate control to trap particulate matter that may escape the production filtration systems in upset conditions was necessary. Prefilters providing sub-micron particulate capture to a minimum efficiency reporting value level of eight also were installed.
- Preventing sulfuric acid corrosion post-combustion. Feed additives such as sulfur-based amino acids eventually end up in the air streams from the reactor/dryers. To ensure the sulfur remains in the gas phase during the oxidation process, it was important to determine a post-combustion temperature that would prevent the formation of sulfuric acid condensation.
The air streams from each fully enclosed reactor/dryer, conveyor, and dust collection system at the facility are ducted to one of three recuperative thermal oxidizers. The 18,000 standard cu ft per minute (SCFM), 13,000 SCFM and 10,000 SCFM thermal oxidizers destroy the sulfur-based VOCs and ammonia emissions from the process with 99.5% destruction efficiency (DRE) and 70% thermal efficiency.
Recuperative Thermal Oxidizers
The recuperative thermal oxidation process begins as the odorous and VOC laden process exhaust is drawn into the thermal oxidizer and directed into the condensate evaporate section where it is preheated to eliminate any vapor droplets before entering the floating tube primary heat exchanger.
This step protects the leading edge of the heat exchanger from condensate build-up and subsequent preignition. When the stream enters the floating tube heat exchanger, it is continuously preheated close to the ignition temperature before being sent to the preheat burner. The exchange of energy in the primary heat exchanger makes up the basis for fuel savings and economical operation.
A preheat burner is used to maintain the combustion chamber operating temperature. The burner is designed to provide the highest degree of flame impingement and high-velocity mixing of the exhaust gases with oxygen, leading to airflow and temperature uniformity.
The contaminated air stream then passes through an elongated high velocity combustion chamber where continued mixing action assures proper mixing of all the effluent constituents. Once mixed, the air stream is held in the dwell chamber long enough to ensure complete combustion of the VOCs. From there, the clean stream passes over the floating tube primary heat exchanger prior to being discharged to the atmosphere or to auxiliary heating systems, such as secondary air-to-air recovery, air-to-water recovery, air-to-oil recovery, or directly back to the process in a closed loop direct recirculation process.
Recuperative thermal oxidizers from CPI feature:
- Round Modular Design: A round design protects against stress and fatigue commonly found in systems that utilize a square box design.
- Internally Insulated: A specialized internal insulation system designed to retain heat for low cost and cool shell temperatures. The internal insulation works in conjunction with the round design to eliminate shell growth for uptime reliability and low maintenance.
- Floating Tube Primary Heat Exchangers: Damaging thermal-mechanical stresses inherent in every thermal oxidizer are eliminated with the round design. The modular design removes the heat exchanger from the combustion chamber to allow each component the ability to individually control growth. The modular design is key to long equipment life and uptime reliability.
- Center Combustion Tube & Burner: The center combustion tube coupled with the preheat burner allows the system to operate at the lowest temperatures while providing the highest VOC destruction. Maximizing turbulent mixing, flame impingement and temperature uniformity provides lower costs and high destruction.
- Temperature Safety System: This system optimizes fuel efficiency by managing temperatures, controlling drives, and positing valves for optimal performance, safety and reliability.