- Thermal Oxidizers System



Thermal oxidizers reduce air pollution emissions from a variety of industrial processes. Using the principle of “thermal oxidation,” a combustion process, the contaminants within the polluted exhaust gas react with oxygen in a temperature controlled environment. The chemical oxidation reaction destroys the contaminants in the polluted exhaust gas before discharging it back into the atmosphere. What is released is an innocuous emission of CO2, water vapor, and heat.

PCC thermal oxidizers operate on the principle mentioned above, which is thermally promoting an oxidation reaction between the pollutant compound in the exhaust gas and the available oxygen. We supply two types of the Thermal Oxidizers: direct fired (afterburner) and recuperative thermal oxidizers.

1. Direct Fired Thermal Oxidizer – The simplest type of thermal oxidizer, it does not include any type of heat recovery system to recover a portion of the waste heat generated by the combustion process. A direct fired thermal oxidizer system typically includes:

  • Burner
  • Combustion chamber
  • Blower
  • Air/fuel train
  • Instrumentation and controls
  • Exhaust stack

Typically less expensive than other types of thermal oxidizers, direct fired thermal oxidizers will incur higher operating cost (fuel use) for waste streams that are endothermic (see Figure 1).

Recuperative Thermal Oxidizer (Afterburner) – Basically, this system is a direct fired thermal oxidizer with heat recovery added at the discharge end of the combustion chamber. Recuperative thermal oxidizers incorporate downstream heat recovery equipment, such as gas- to-gas heat exchangers, waste heat recovery boilers, gas to liquid heat exchangers, etc… to maximize the thermal oxidizer system overall efficiency.

Downstream heat recovery equipment uses the available heat produced within the thermal oxidizer combustion chamber to reduce auxiliary fuel consumption, produce steam, heat a process air stream, or heat a liquid stream. A recuperative thermal oxidizer system can have a single heat recovery device (Figure 2), or multiple heat recovery devices (Figure 3).

In addition to the recuperative thermal oxidizer systems shown above, a recuperative thermal oxidizer can incorporate:

  • Combustion air preheat to conserve fuel
  • Other heat recover equipment such as a hot oil heater, hot water economizer, or asphalt heater

Recuperative thermal oxidizers can treat multiple gaseous and liquid waste streams that are endothermic and/or exothermic.

Our core engineering staff is experienced in process engineering, material selection, refractory design, structural design, and controls and instrumentation. With degrees in various engineering disciplines, our Professional Engineers (P.E.) are also registered in several states.

We’ve custom designed more than 1,000 systems for Fortune 500 companies of all sizes– and we have an excellent track record for performance and reliability. Here are some of our typical applications.

Typical Wastes

  • Acrylonitrile
  • Terephthalic Aced
  • Butanediol
  • Mercaptaines
  • Low BTU Gases
  • VOC’s
  • Waste Oils
  • Butyl Chloride
  • Phosphine
  • Hydrogen Cyanide
  • Toluene
  • Benzene
  • Halogenated Hydrocarbons
  • Trichloropropene
  • Maleic Anhydride
  • Dibutyl Phthalate
  • Trifluoroacetic Acid
  • Chloridated Hydrocarbons

We serve industries including:

  • Chemical    
  • Converting
  • Petrochemical    
  • Metals
  • Refining    
  • Food
  • Automobile    
  • Wood products
  • Pharmaceutical    
  • Sulfur
  • Manufacturing    
  • Carbon
  • Textile    
  • Pulp and paper
  • Rubber     

Emissionscontrol and the vital role of thermal oxidizers.

Thermal oxidizers have played a vital role in Emissions Control Permitting since the Clean Air Act Amendments of 1990. By reducing the levels of pollutants that are released to the atmosphere thermal oxidizers are effective in the destruction and removal of more than 80% of the 189 specified Hazardous Air Pollutants under the CAA.

Along with identifying this list of 189 toxic air pollutants, the Clean Air Act Amendments (CAA) of 1990 established programs that set limits on how much of a pollutant can be in the air anywhere in the United States. In order to achieve the pollution limits, the CAA created an Emissions Control Permitting program for larger stationary sources.

What does the Clean Air Act mean for business owners?

Under the program, owners of sources are required to obtain an Emissions Control Permit from the state in which it resides.

The Emissions Control Permitting process forces owners to:

  • Monitor and measure the amount of pollutants that are released from each source
  • Provide information about which pollutants and the quantity of pollutants that may be released
  • Reveal steps taken to reduce the amount of pollution

Theimportant issue of VOC destruction and removal.

Many industrial processes emit volatile organic compounds (VOC’s). Due to the role of this compound in air pollution, VOC destruction and removal is a prominent issue in our society.

Along with identifying this list of 189 toxic air pollutants, the Clean Air Act Amendments (CAA) of 1990 established programs that set limits on how much of a pollutant can be in the air anywhere in the United States. In order to achieve the pollution limits, the CAA created an Emissions Control Permitting program for larger stationary sources.

In response to this growing concern, the Clean Air Act Amendments (CAA) of 1990 were passed. These amendments changed the focus of air pollution from a set of six “priority pollutants” to the control of VOC’s. The CAA is intended to reduce the emissions of VOC’s by 70-90%. Subsequent legislation has also been passed to further reduce the emissions of VOC’s to the atmosphere.

VOC destruction and removal rates greater than 99.99%.

Since the inception of the 1990 Clean Air Act, thermal oxidation systems have continued to play one of the most important roles in VOC destruction and removal, due to its ability to destroy the VOC’s in a one-step process while producing innocuous by-products.

A properly designed thermal oxidizer system can achieve VOC destruction and removal rates greater than 99.99%.

Other advantages of thermal oxidation include:

  • Ease of operation and control
  • Ability to be altered for process variations
  • Continuous process
  • Elimination of by-product disposal
  • Number of process components
  • Ability to be applied to more than 80% of the CAA Air Toxics

Industries for which thermal oxidizers have been used for VOC destruction and removal include, but are not limited to:

  • Petrochemical
  • Man-made Fibers
  • Petroleum
  • Pulp & Paper
  • Automotive
  • Energy
  • General Manufacturing
  • Pharmaceuticals
  • Animal Rendering

Wasteheat boilers recover energy and conserve fuel.

PCC specializes in designing and engineering fully integrated thermal oxidizer systems. Many times that includes downstream heat recovery equipment along with additional downstream pollution control equipment, as required for the specific pollution control application.

PCC recuperative thermal oxidizers integrate a waste heat boiler into the complete system. If the application is such that the end user needs a thermal oxidizer system for pollution control and also has a need for steam, adding a waste heat boiler to the thermal oxidizer system is a highly effective way to recover energy that would otherwise be discharged to atmosphere. Typically, the waste heat boiler is located after the thermal oxidizer combustion chamber. The primary function of the waste heat boiler is to utilize the thermal oxidizer hot products of combustion to generate steam, which can be utilized within the end users production process, within their building facilities, within the thermal oxidizer system itself, or even sold to neighboring facilities that need steam. All of these options result in a financial benefit for the end user, because their steam requirements are satisfied using the waste heat boiler without the added capital and operating expense associated with a separate direct fired boiler system.

A waste heat boiler recovers additional energy recovery and fuel conservation by:

  • Adding a boiler feed water economizer to the waste heat boiler. The boiler feed water economizer is basically a gas-liquid heat exchanger located after the boiler evaporator section. The economizer also uses a portion of the energy contained in the thermal oxidizer combustion gases (after the waste heat boiler) to preheat the boiler feed water before it enters the boiler evaporator section.
  • Using excess steam produced by the waste heat boiler to preheat a waste gas or combustion air stream coming to the thermal oxidizer system. A waste gas or combustion air steam pre-heater uses the excess steam from the waste heat boiler to preheat these streams prior to entering the thermal oxidizer. This reduces the thermal oxidizer auxiliary fuel use and therefore reduces the overall system operating costs.

Typical waste heat boilers used on thermal oxidizer applications include firetube boilers and watertube boilers.

Firetube boilers – Generally for smaller applications, where the thermal oxidizer system heat release is below 20 MM Btu/hr and when high pressure steam is not required.

Watertube boiler – More suitable for larger applications with high pressure steam requirements.

Countless configurations and the expertise to recommend them.

So many options… our experts will help you chose the most effective one.

There are many different process configurations available for integrating a waste heat boiler into a recuperative thermal oxidizer system. PCC has supplied recuperative thermal oxidizer systems with a waste heat boiler as the primary heat recovery device followed by multiple heat recovery devices such as combustion air and waste gas pre-heaters.

Careful analysis of emission and steam requirements, process operating conditions, and operating cost objectives is our expertise. We’re here to help.

Thermaloxidizer design and how to choose the right supplier.

Virtually every industrial manufacturing process results in waste products— cause for concern in today’s environment. Thermal oxidation has proven through the years to be an effective and safe method for the disposal of a wide variety of industrial wastes if proper thermal oxidizer design practices are followed.

Thermal oxidizer design can be relatively straight forward or complex depending on the application, waste characteristics, and the air permit emission requirements. Most thermal oxidizer designs incorporate similar design principles to ensure that the desired oxidation reaction occurs and the waste stream contaminants are reduced to the levels necessary to achieve emission compliance.

Here are typical thermal oxidizer design inputs and outputs.

Typical Design Inputs:

  • Upstream process operating conditions (batch or continuous process)
  • Full range of process operating conditions (Max., Min., Norm., Start-up, Upset, Design, etc.)
  • Waste stream design parameters (flows, pressures, and temperatures)
  • Waste stream composition and variability
  • Available utilities, site conditions and physical equipment constraints

Typical Design Outputs:

  • Air emission limits (CO, NOx, VOC, SOx, HCl, PM, etc.)
  • Performance requirements (fuel consumption, reliability, noise, etc.)

Step 2

Begin thermal oxidizer design process.

Once these parameters are defined, the thermal oxidizer design process can begin. A basic thermal oxidizer system consists of a refractory lined vessel known as the thermal oxidizer, a burner, stack, and combustion controls.

The Three T’s” of Combustion.

These are required in order to achieve successful thermal oxidation:

  1. Turbulence – Thorough mixing
  2. Temperature – Oxidizing temperature (typically 1200°F – 1650°F)
  3. Time – Combustion chamber residence time (typically 0.5 seconds – 2.0 seconds)

The Three T’s of Combustion, along with sufficient oxygen, are essential and interrelated in all thermal oxidizer designs. The level of turbulence (mixing), the necessary reaction temperature, and the amount of time (residence time) is primarily dependent on the waste stream characteristics and the level of destruction required for achieving the specific air permit compliance.

PCC custom designs all of our thermal oxidizer systems. Our extensive industrial application experience coupled with our experience in handling a wide spectrum of waste streams, give us the expertise to determine how best to incorporate the Three T’s of Combustion into each thermal oxidizer design.

Step 3

Determine essential design features.

As we mentioned, a basic thermal oxidizer system includes a refractory system, burner, exhaust stack, and combustion controls. More complex thermal oxidizer systems include heat recovery such as gas to gas heat exchangers and waste heat boilers, plus additional downstream pollution control equipment such as scrubbers, particulate filters, and wet ESP’s. Each of these components have a variety of important design features (too extensive to discuss here), which must be considered to ensure the complete thermal oxidizer “system” is safe, reliable, and meets all performance objectives.

Other important factors to consider when evaluating a thermal oxidizer supplier:

  1. Experience level with the specific application
  2. Industry reputation
  3. Process design capabilities
  4. In-house expertise
  5. Project execution and delivery reputation
  6. Services (installation, start-up, training, routine maintenance, etc.)
  7. Financial strength

Step 4

Learn more.

Discover why PCC is the right choice for your next thermal oxidizer system. Contact us directly at (412)

Whatis an industrial waste incinerator?

Any device or system that uses combustion and/or thermal oxidation to destroy or reduce an industrial waste can be classified as an industrial waste incinerator. Most commercial, industrial, municipal and institutional wastes are classified by composition and heating value.

In 1968, the Incinerator Institute of America used general classifications to define waste streams. While these classifications are broad and somewhat outdated (the definition and composition of these waste streams have changed with advances in technology, products and services), they still serve as a reference for industrial waste incinerators.

Waste classifications defined.

Type 0 Waste – Trash consisting of highly combustible waste paper, wood, cardboard cartons and including up to 10% treated papers, plastic or rubber scraps from commercial and industrial sources. Type 0 Waste has a heating value of 8,500 Btu per pound, a moisture content of 10% (by weight) and an ash content of 5% (by weight).

Type 1 Waste – Rubbish consisting of combustible waste paper, cartons, rags, wood scraps, combustible floor sweepings from domestic, commercial and industrial sources. Type 1 Waste is a mixture of 80% (by weight) rubbish and 20% (by weight) garbage. It has a heating value of 6,500 Btu per pound, a moisture content of 25% (by weight) and an ash content of 10% (by weight).

Type 2 Waste – Refuse (Municipal Solid Waste) consisting of rubbish and garbage from residential sources (50% rubbish and 50% garbage). Type 2 Waste has a heating value of 4,300 Btu per pound, a moisture content of 50% (by weight) and an ash content of 7% (by weight).

Type 3 Waste – Garbage consisting of animal and vegetable food wastes from restaurants, hotels, markets, institutional, commercial and club sources. Type 3 Waste is a mixture of 65% garbage and 35% rubbish. It has a heating value of 2,500 Btu per pound, a moisture content of 70% (by weight) and an ash content of 5% (by weight).

Type 4 Waste – Pathological Waste consisting of 100% animal and human tissue. The principal components are carcasses, organs, solid organic wastes from hospitals, laboratories, abattoirs, animal pounds and similar sources. Type 4 Waste has a heating value of 1,000 Btu per pound, a moisture content of 85% (by weight) and an ash content of 5% (by weight).

Type 5 Waste – Industrial process wastes including gaseous, liquid or semi-liquid wastes. The composition, heating value, moisture content and ash content of Type 5 Wastes are variable and must be confirmed by a waste analysis.

Type 6 Waste – Semi-solid and solid combustible wastes which require hearth, retort or grate burning equipment. The composition, heating value, moisture content and ash content of Type 6 Wastes are variable and must be confirmed by a waste analysis.

PCC designs, fabricates and supplies industrial waste incinerators that safely and efficiently destroy many types of gaseous and liquid wastes (type 5 wastes as outlined above).

Post-CombustionNOx Reduction… SNCR or SCR?

PCC puts our proprietary technology and combustion processes know-how to work selecting the optimum burner(s), system configuration, process design, and operating conditions to meet the specified NOx emission limits. All NOx generation methods – “thermal NOx formation”, “chemical NOx formation” and “prompt NOx formation” are evaluated when determining whether low NOx burners, staged air systems, staged fuel systems and/or multi-stage combustion systems are required to achieve low NOx emissions.

What if fuel-bound nitrogen is present?

In certain situations, combustion techniques, process changes and modifying operating conditions might not meet the specified NOx emission limits. In these case, NOx emissions can be met by adding one of two post combustion NOx reduction processes:

  1. Selective Non-Catalytic Reduction (SNCR)
  2. Selective Catalytic Reduction (SCR)

When necessary, PCC incorporates the appropriate post combustion NOx reduction technology (SNCR or SCR) into our thermal oxidizer systems. We custom design and supply the complete SNCR or SCR package. We can also design and supply “stand alone” SNCR or SCR systems for new or existing combustion systems.

Ammonia-based process details.

In this SNCR process, ammonia vapor carried by an air stream or steam is injected into the flue gas at the appropriate temperature zone, 870°-1200°C (1600°-2200°F), effecting a reduction of NOx to nitrogen and water.

The injection of ammonia into flue gas leads to a complexity of intermediate chain branching reactions. The following two simplified chemical equations summarize the overall process:

Equation 1 – 2NO + 4NH3 + 2O2 = 3N2 + 6H2O

Equation 2 – 4NH3 + 5O2 = 4NO + 6H2O

Equation 1 is the NOx reduction reaction which occurs in the 870°-1200°C (1600°-2200°F) temperature range by the injection of ammonia alone. NOx reduction effectiveness can be enhanced down to 700°C (1300°F), by injection of hydrogen (H2 along with NH3). However, as indicated by Equation 2, the injection of NH3 into high temperature flue gas results in increased NOx formation and is thus counterproductive.

For initial NOx levels of 200 ppmvd or less, NH3/NOx molar ratios of about 1.5 are commonly used.

Urea-based process details.

This SNCR process uses urea, CO (NH2)2 as a reducing agent. It injects an aqueous urea solution into the path of the NOx laden combustion products. The urea thermally decomposes to produce chemical species which react with NOx to form nitrogen, carbon dioxide, and water.

Equation 3 – CO (NH2)2 + 2NO + 1/2 O2 = 2N2 + CO2 + 2H2O

Equation 4 – 4NH3 + 5O2 = 4NO + 6H2O

In Equation 3, it follows that the stoichiometric molar rate of urea relative to NO in the combustion products is 0.5, since one mole of urea potentially has two moles of NH2 available to react with NO. The urea injection process for NOx control is also temperature sensitive. The urea solution, therefore, must be injected in the temperature range of 870°-1200°C (1600°-2200°F).

Factors that influence NOx reduction efficiency.

The NOx reduction efficiency of both SNCR processes depends on the following factors:

  • Flue gas temperature in reaction zone
  • Uniformity of flue gas temperature in the reaction zone
  • Normal flue gas temperature variation with load
  • Residence time
  • Distribution and mixing of ammonia/urea into the flue gases
  • Initial NOx concentration
  • Ammonia/urea injection rate
  • Heater configuration, which affects location and design of injection nozzles

SCR defined.

The selective catalytic reduction process removes nitrogen oxides (NOx) from flue gases by injecting ammonia (NH3) into the flue gas and passing the well mixed gases through a catalyst bed. NOx reacts with NH3 in the presence of the catalyst to produce nitrogen (N2) and water (H2O) as shown in the following equations.

Equation 5 – 4NO + 4NH3 + O2 = 4N2 + 6H2O

Equation 6 – 6NO + 4NH3 = 5N2 + 6H2O

Equation 7 – 2NO2 + 4NH3 + O2 = 3N2 + 6H2O

Equation 8 – 6NO2 + 8NH3 = 7N2 + 12H2O

Equation 9 – NO + NO2 + 2NH3 = 2N2 + 3H2O

Note that the first reaction for refinery applications generally dominates since 90% of the NOx is NO. A wide variety of available catalysts can operate at flue gas temperature windows ranging from 165°–600°C (325°–1100°F). High NOx reduction efficiencies can be achieved if the parameters such as residence time, space velocity, and the correct temperature window are controlled.

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