Oxidizers are emission control systems that process exhaust air stream by burning or oxidizing combustible solids or liquids present in the stream, and then release the toxic-free gases into the atmosphere. The principle is simple: instead of selectively filtering out the toxic particles, they burn them all. They are used to effectively remove Hazardous Air Pollutants (HAP), Volatile Organic Compounds (VOC), and recently Particulate Matter (PM).
While oxidizers do not inherently eliminate all contaminants and particulates in an air stream, byproducts of the reaction are non-toxic and more easily managed after oxidization than the original pollutants. The complex machines are often very large and are therefore more applicable in industries that yield high emissions such as paper and pulp, agriculture, printing, food processing, polymer and resin manufacturing, pharmaceuticals, painting and more. Not all oxidizers are so cumbersome, however, as they are also implemented in automotive exhaust systems. The volume and solvent load of the process air stream should be carefully considered when selecting an oxidizer as is the typical temperature range of a system. All of these factors have a significant impact on the destruction efficiency of an oxidizer which is generally between 90% and 99%.
Quick links to Oxidizers Information
Operation of Oxidizers
Though highly specialized, the basic operation of oxidizers is not overly complicated. An air stream that has been polluted by industrial processing is forced into the main chamber of an oxidizer. The materials are heated to the point where incineration or a chemical reaction occurs, burning and converting the harmful solids or liquids into less harmful byproducts which may then be filtered or collected for disposal. There are two main types of oxidizers, thermal and catalytic. Thermal oxidizers may be regenerative or recuperative with regards to heat transfer and retention. This is essential to lowering operational costs as thermal oxidizers use very high heat to incite combustion of contaminants. Catalytic converters likewise break down hazardous compounds, but do so at a much lower temperature. To accomplish this, a noble metal catalyst, such as platinum or palladium, is used to promote oxidation within the combustion chamber. Oxidizers that make use of a rotor concentrator are also growing in popularity. These oxidizers process air flows through a continuously rotating wheel impregnated with adsorbent agents. The type of oxidizer chosen depends largely on the operating space and capacity as well as the specific contaminants in a process stream. Selection should be made carefully to ensure the highest destruction efficiency possible which results in diminished atmospheric pollution.
Advantages and Disadvantages of Regenerative Oxidizers
Advantages of Regenerative Oxidizers
- They can achieve efficiency as high as 95 percent, which is unparalleled.
- For processing air streams lower amount of fuel is required, as the high amount of energy is recovered by the system.
- The temperature can reach up to 2000 ° F, which provides great destruction efficiency, in comparison to conventional recuperative incinerators, which, in general, operate at 1500°.
- The heat exchanging capability is far better than recuperative catalytic incinerators.
- They can withstand problems related to chlorinated compounds, which proves to be a major hurdle for other designs available.
- The emission of oxides of nitrogen is lower in comparison to thermal oxidation.
- When the regenerative technology is used in catalytic oxidizers (RCO), it lowers the fuel consumption, as lower temperature is required. Moreover, RCO can obliterate carbon monoxide, which is hard to achieve in different systems.
Disadvantages of Regenerative Oxidizers
- The upfront investment cost is high.
- The installation can be difficult.
- Relatively large in size and heavier in weight.
- All moving parts demand high maintenance.
- However, among all emission control systems, regenerative thermal oxidizer is the most efficient system. Once they are installed, high flow and low concentration waste streams can be treated consistently over long periods, economically.
Types of Oxidizers
Primarily, oxidizers are divided based on the principle they employ to oxidize particles: thermal oxidizers and catalytic oxidizers.
- Thermal Oxidizers
- Use plumes of fire to incinerate the combustible organic or inorganic pollutants, which are present in the stream. The decomposition of hazardous gases occurs at extremely high temperatures, in the range of 800°F to 2000°F. Thermal oxidizers are further divided as afterburner, also known as direct-fired thermal oxidizer, regenerative thermal oxidizer (RTO), and thermal recuperative oxidizer.
- Catalytic Oxidizers
- Also called as catalytic incinerators, work in the similar way to that of thermal oxidizer, however, catalytic oxidizers utilize catalysts for promotion of the oxidation process, or burning of pollutants. With the presence of catalyst to accelerate the rate of combustion, the contaminants can be disintegrated at significantly lower temperature range, from 644 °F to 1,004 °F. The catalysts are precious metal, typically platinum and rhodium, in the form of a bed, which promotes the oxidizing reaction.
- Direct-Fired Thermal Oxidizer
- In an afterburner, the simplest of thermal oxidizers, hazardous gases mixed in the stream are exposed to a firing box. To burn the organic compounds, the gases remain in the burner for predetermined time, known as residence time, to maintain high efficiency. To obtain the destruction removal efficiency, afterburners function at very high temperatures, between 1,800 F and 2,190 F, at air flow rates that range from 0.24 to 24 standard cubic meters per second.
- Regenerative Thermal Oxidizer
- RTOs are modern air pollution control incinerators designed to reclaim the heat from the oxidizing process. In this type of oxidizers, the stream is not directly exposed to the combustion temperature, but a ceramic bed is employed to preheat the gases before entering the combustion chamber, which is used as fuel source to oxidize the gases. It works in the temperature range of 1,400 °F to 1,510 °F, far below direct-fired oxidizers.
- Thermal Recuperative Oxidizer
- They too are designed to reclaim heat from the oxidization process; however, they utilize heat exchangers instead of a ceramic bed. Either a tube and shell heat exchanger or plate heat exchanger is utilized to preheat the incoming exhaust stream. The design recuperates the heat from the leaving clean air to preheat the incoming air. They, at present, are less popular than regenerative oxidizers, as they are often less efficient.
The major source of air pollution is the industrial emission. To regulate the release of hazardous gases of different types to the atmosphere, ranges of pollution control equipment are available, such as oxidizers, air and wet scrubbers, electrostatic precipitators, vacuum cleaners, and mist collectors, and wet scrubbers. Each of the devices is designed for air pollution control of different poisonous gases and particulates, based on the application, from the exhaust air streams of stationary sources. Most of them, however, have not evolved enough yet to add any production value. Nevertheless, some have, like regenerative oxidizer, which widely has been used to reclaim heat from the processing of exhaust to fuel other processes, within the facility.
Regenerative Oxidizer Applications
Regenerative oxidizers have application in a variety of stationary sources. However, they best suit the units that have high flow—greater than 2.4 standard cubic meters per second or 5,000 standard cubic feet per minute—and low volatile organic compound (VOC) concentration—less than 1000 parts per million by volume. Generally, such types of discharge attributes are found in:
- Automotive Manufacturing
- Wood Products Manufacturing
- Coating and Metalworking Operations
The regenerative oxidizers also have application in removal of condensables and Particulate Matter (PM). Although, internal filters or some pretreatment technology is required to catch bigger particles before the air stream enters the reactor chamber, as PM and condensables generally choke the incinerator’s bed.
Regenerative catalytic oxidizers are also available that effectively remove volatile organic compounds as well as bromides, chlorides, and other halogens. They are considered not suitable when the stream contains phosphorus, silicon, arsenic, and other heavy metals, as they act as the poisoning agents.
Inarguably oxidizers are the most common pollution control equipment that can be spotted at a number of industrial facilities. However, do you know how they are categorized or how many types of oxidizers are available? Here in this blog we are discussing all that.
Oxidizer Standards and Safety Specifications
As oxidizer intensifies combustion, widens the flammable range of inflammable liquids and gases liquids, and lowers the ignition temperatures, it poses a serious fire hazard. Moreover, the combustion products of oxidizers and similar pollution control equipment, in general, can be more toxic. The most cited example is the oxidation of chlorine related pollutants that liberates carbon tetrachloride vapor and hydrogen chloride gas. Inhalation of hydrogen chloride gas can lead to corrosion of lung tissue and other related mucous membranes. This can transform into pulmonary edema, asymptotically.
As thermal oxidizers oxidize the combustible pollutants in the exhaust stream, soft tissues, including skin, eyes, and lung are always at great risk. The risk gets higher, when acids are oxidized. The exposure of skin to oxidizing products can result in hazardous burns, as well as dermatitis, where skin loses its moisture and gets dry. Dermatitis is more common. The danger to soft tissues from other oxidizers depends on the type of oxidizer and concentration of the oxidizing agents in the air-pollution control system. Evidently, the combustion products of oxidizer like emission control systems are harmful; therefore, general mitigation measures need to be followed. Here in this blog, we are discussing those mitigation measures:
- The primary measure is to conduct a systematic literature search and come to know about the safety data sheets, which can be availed through various resources. The research will help you to understand the properties and attributes of a given oxidizer. You will learn about the procedures and tasks to be conducted before operation. The knowledge of reactive and energetic compounds, which are released during oxidation, will help to device protective measures.
- At the plant, all employees should be trained about the general safe chemical handling practices, related to chemical ordering, distribution, storage and usage. Moreover, establish all safety procedures for the procedure at the facility.
- Combustible materials, including wood, paper, finely divided metals, greases, oils, flammable and combustible liquids, and all oxidizable substances, such as phosphorus and hydrides should be kept away from the processing unit. Sometimes, incompatible substances can create problems, thus, it is a good practice to keep all unnecessary materials away from the work area.
- All employees working near the oxidizing unit should wear personal protective equipment, including flame retardant lab, as they help to withstand chemical exposures.
- It is advised to conduct work, if possible, on a small scale, as it helps to control hazard-contributing factors.
- When compressed oxidizing gases are involved, the auxiliary equipment, such as valves, gauges, and piping, must comply with the standards. All these equipment must be free from other materials, especially, oil and grease, which are hydrocarbon based materials.
- When oxidizing gases are used, the facility should be well ventilated. Moreover, if possible, only diluted solutions of oxidizers are used, as it reduces reactivity, thus, health hazards.
- If lab coats, paper towels, and clothing, which are categorized as combustible solids, are contaminated with oxidizers, they should be soaked and rinsed with water for removing the oxidizer.
- All reactive oxidizer mixtures should be used only inside the established temperature ranges. Many times, they have been proved a source of explosive reactions.
- All facilities should be fitted with fire extinguisher measures and functioning safety showers.
Proper Care for Oxidizers
Oxidizers are chemical reactions that readily yield oxygen or vigorously promote oxidation reactions or the combustion of organic and typically non-flammable materials. Though this is the popular scientific explanation, the term is also applied to emission control systems which operate using the chemicals known as oxidizers to reduce or eliminate harmful pollutants in an air stream. Incineration or chemical reactions that occur in these systems reduce pollutants such as volatile organic compounds (VOCs), converting them into carbon dioxide, water and nitrogen.
Oxidizers play a crucial role in many applications when it comes to air pollution control for industrial companies. Because of the important task they complete, maintaining the operating performance of oxidizers is often a high priority. The following are some helpful tips to make certain that you and your company are getting the most out of your oxidizer as this will prevent the need for repairs and other unnecessary slow-downs in the future. Maintaining the system consistently throughout the year, and particularly in the winter months, is recommended to ensure the oxidizer’s overall reliability. One of the simplest things you can do is to regularly do a visual once over of the system, checking equipment for splits, cracks, debris or discoloration. Installing a desiccant-style dryer for the compressed air supply is also recommended in order to avoid moisture build-up. It is also a good idea to stock spare parts as this will greatly reduce downtime if a component does happen to fail.
Obviously, it is also important to follow regular maintenance schedules listed in standard operating manuals. Having a combustion technician fine tune the unit each year is also highly recommended to get your system back on track and operating at the highest performance level. This task could also catch potential failures and correct them before major repairs are required, thus saving time and money in the long run. There are also usually options for programs that offer real time system information, user friendly troubleshooting, and higher levels of energy efficiency. Again, it is also important to investigate the desiccant dryer and compressed air lines for leaks and condensation. Don’t slack on preventative maintenance and pay for it later. Secure the working order of your oxidizer system by performing continual inspection and maintenance throughout the year.