12 Incinerator Types, their Pros and Cons Explained
An incinerator or incineration plant is a system designed to facilitate the combustion and thermal decomposition of materials like municipal solid waste (MSW) and biomass. The main incinerator types are drum, single-chamber, dual-chamber, fluidized bed, rotary kiln, fixed grate, moving grate, catalytic combustion, liquid injection, pyrolytic, waste gas flare, and specialized incinerators. They are discussed in this article according to the following outline;
-Incinerator Types and the Factors used in their Classification
-Advantages and Disadvantages of the Various Types of Incinerators
Incinerator Types and the Factors used in their Classification
The types of incinerators are liquid injection, fluidized bed, rotary kiln, catalytic combustion, specialized, single-chamber, dual-chamber, waste-gas flare, fixed grate, moving grate, and drum incinerators.
Factors used to classify these types of incinerators include geometry, purpose, interior design (number of chambers, motion of parts), mode of operation.
The individual types of incinerators are discussed below, within the context of the factors used to classify them;
Incinerator Types Based on Geometry and Interior Design
1). Drum Incinerator
This is one of the simplest types of incinerators in terms of design and operation.
The drum incinerator consists of a sealed drum or barrel into which waste is introduced and subsequently burnt in a supply of oxygen.
It is a fairly simple set up, and the drum may be symmetrical or tapered depending on the need. Similarly, the size of the drum and the amount of heat and oxygen supplied may vary. The lid itself may be either solid or in grid form.
Drum incinerators are ideal for small-scale use, such as for burning personal garden waste, papers, or other materials.
This type of incinerator has the disadvantage of being a major cause of air pollution when used. Other types of incinerators may perform better due to the presence of equipment that can mitigate the production and release of toxic byproducts.
When wastes with high calorific value are burnt using the drum incinerator, there is often unsteady combustion [8], which reduces the effectiveness of the incineration process.
2). Single-Chamber Incinerator
Single-chamber incinerator is a type of incinerator which depends on one cycle of combustion to treat waste.
Unlike most other types of incinerators, this type is usually equipped with only one burning chamber or vessel.
The chamber may occur as a permanent and simple furnace constructed from solid material like concrete, and which encloses a fixed grate.
In order for complete combustion to be achieved, air may be injected into the chamber.
Basically, any incinerator with one combustion chamber or vessel can be described as a single-chamber incinerator. This will include types like the drum incinerator [13].
Because of its technical limitations, the single-chamber incinerator is not widely used and may not meet environmental conservation guidelines.
3). Dual-Chamber Incinerator
Based on geometry and interior design, various other types of incinerators can be classified under this category.
The dual-chamber incinerator comprises of a primary and secondary combustion chamber, which are responsible for incinerating non-gaseous gaseous materials respectively.
Dual-chamber incinerators operate based on a two-stage process. In the first stage, waste (fuel) is introduced into the primary chamber where it undergoes combustion [7].
During this initial stage of combustion, gaseous byproducts may occur as the waste is thermally decomposed.
These gaseous byproducts (may be collectively called ‘flue gas’) are introduced into the secondary chamber in the second stage.
During the second stage, gaseous substances produced in the first stage are broken down in another phase of thermal decomposition. Usually, the end products of the overall process are relatively-simple compounds.
To improve the efficiency of dual-chamber incinerators, both chambers may be equipped with air-control systems to regulate the amount of oxygen that enters the incinerator. This is usually applied in large or specialized incineration plants.
Like the single-chamber incinerator, the walls of the two chambers are made from solid material such as concrete. The temperature of the system is also usually in excess of 1,000°C [2].
Incinerator Types Based on Mode of Operation
4). Fluidized Bed Incinerator
In the fluidized bed incinerator, a sand bed is kept in suspension by a pressurized, vertical stream of air [3].
The air stream is usually preheated, and when waste is introduced into the incinerator, this heat is transferred to the waste, resulting in thermal decomposition.
Because of the agitated state of the sand bed and waste; the entire system occurs in a state that is similar to a condition of fluidity. In many cases, this improves the overall effectiveness of the incineration process.
5). Rotary Kiln Incinerator
Rotary kiln incinerator comprises of a cylindrical steel vessel internally lined with refractories, which is inclined and rotates on its axis.
Waste is introduced into the vessel from its top, and heated to temperatures which may be up to 1600°C, to allow thorough thermal decomposition to occur.
The cylindrical vessel generally rotates at a slow pace [6], and this causes the waste to move, allowing for sufficient oxygen to be introduced.
Protection from heat-induced damage is provided by the refractory layer, which shields the metal walls of the vessel from the direct effect of extreme heat.
Like other types of incinerators, the rotary kiln incinerator may have varying designs and capacities that depend on the specific needs of the waste treatment project.
One of the uses of this incinerator is to treat heterogenous (mixed) hazardous and industrial waste.
6). Fixed Grate Incinerator
The fixed grate incinerator consists of a metal grate which is in a fixed position over a heat source, and enclosed by solid walls.
Arguably, fixed grate incinerator is one of the simplest types of incinerators.
Waste may be introduced through the side or top of the enclosure, and the system performs thermal destruction of this waste, by combustion.
The fixed grate incinerator is suitable for waste which is easy to oxidize and combust, and can be used to decompose gaseous substances as well.
An example of the latter is the use of fixed grate incinerator to address odor and smoke-oil mist challenges during rubber-base rug manufacturing.
Because of the configuration of this type of incineration system, it may be a good choice when flexibility in terms of heat application and waste introduction/removal, is desired.
7). Moving Grate Incinerator
Also known as ‘roller grate incinerator’, the moving grate incinerator is designed to provide a mechanism by which waste can be moved at constant velocity through the combustion chamber, on a series of inclined mobile grates.
This mechanism allows for effective burning as a result of adequate exposure to heat and oxygen.
In many moving-grate incinerators, the waste can be removed from the combustion chamber after it has been treated, making it to be one of the most potentially productive types of incinerators.
A common use of the moving grate incinerator is for the treatment of municipal solid waste (MSW). In developed regions like the UK, the moving grate concept is one of the most common concepts based on which direct waste-combustion is carried out [12].
The moving grate incinerator is capable of being used to treat a broad range of waste volume and calorific value. It can also be operated at various temperatures, depending on the specific need.
8). Catalytic Combustion Incinerator
A catalytic combustion incinerator is a waste treatment system which is capable of using a catalyst to improve the effectiveness and efficiency of the incineration process.
The function of this system can be referred to as ‘catalytic oxidation’ because combustion is itself a form of oxidation, and it is enhanced using a catalyst in this case.
Catalysts are often used in cases where the waste contains materials that are complex and/or require complete thermal destruction. When used, these catalysts can reduce the temperature at which combustion occurs [1].
Examples of catalysts used in incineration are palladium, platinum and metallic oxides. Nickel-based compounds can also be used [10].
Uses of catalytic combustion incinerator include solvent emission abatement [9], and conversion of volatile organic compounds (VOCs) like ethylbenzene to carbon dioxide and water [4].
9). Liquid Injection Incinerator
A liquid injection incinerator may occur in the form of a cylindrical chamber that is lined internally with refractories, and which has apertures through which liquid waste can be introduced into the chamber.
This type of incinerator is used for liquid wastes like sewage sludge, and may be used to treat toxic materials like industrial effluents.
The principle used in liquid injection incinerators is thermal degradation of pollutants in liquids through prolonged heating.
In terms of geometry and design, the liquid injection incinerator may occur in any of various forms, such as cylindrical, single-chamber and double-chamber.
10). Pyrolytic Incinerator
A pyrolytic incinerator is a chamber in which thermal decomposition of waste occurs, either in the absence, or in limited supply, of oxygen.
What occurs in a pyrolytic incinerator is very similar to pyrolysis, which is another thermal-based waste-to-energy method like incineration.
However, the two methods differ in that pyrolytic incineration may involve combustion while pyrolysis does not.
In order to allow for combustion when needed, pyrolytic incinerators may be equipped with air-control systems that regulate the oxygen that enters the combustion chamber. Such systems can be found in some other types of incinerators as well.
Variable temperatures can be used in pyrolysis incineration plants. This may range from 800°C to an excess of 1,000°C.
The use of a pyrolysis incinerator is required for specific cases of waste treatment. It is considered to be one of the most effective and commonly-used treatment methods for medical waste [14], and is also very useful for treating organic waste (biomass).
Because of the need to regulate air supply, pyrolysis incinerators generally require a significant degree and frequency of maintenance, compared to other types of incinerators.
Pyrolysis incinerators are also used for analytical purposes and other cases where a specific range of thermal decomposition products are required, as well as for the production of renewable energy in the form of fuels like syngas [11].
Incinerator Types Based on Purpose
11). Waste-Gas Flare Incinerator
Most types of incinerators are equipped with mechanisms and tools to prevent or minimize the release of gaseous byproducts into the atmosphere.
A waste-gas flare incinerator is designed to get rid of flammable gaseous byproducts through flaring, which is a method of controlled burning of gaseous fuels as part of processing and production operations in the energy industry [5].
Waste-gas flare incinerators come with a number of problems. These problems arise mainly from the fact that flaring is a potential cause of environmental degradation.
Toxic gaseous byproducts of incineration may escape in the process of flaring, and may reduce air quality.
Flaring is also a contrary practice to the global efforts to achieve sustainable development, because greenhouse gases like carbon dioxide and methane can be released during flaring, and can contribute to global warming and climate change.
Generally, waste-gas flare incinerators are used only where the waste produces excessive amounts of gaseous byproducts, and/or where there are no facilities to treat or capture gases.
A good alternative to the operational mode of this type of incinerator, is waste-to-energy.
When waste-to-energy practices are incorporated into the incineration plant, the gaseous effluents can be used as fuel for heating, electricity generation, or cogeneration.
12). Specialized Incinerator
A specialized incinerator is basically any incinerator that is designed for a very specific function.
This function may be defined by the type of materials that can be treated using the incinerator, or the mechanism of incineration that is used.
Various types of incinerators can be classified under this category, especially where these incinerators are capable of performing specific functions. To achieve their purpose, the specialized incinerators are usually equipped with some key components.
A common example of a specialized incinerator is the sawdust incinerator used in furniture factories. These are equipped with air-control systems to regulate the combustion of sawdust.
Advantages and Disadvantages of the Various Incinerator Types
| Incinerator Type | Advantages/Pros | Disadvantages/Cons |
| Drum Incinerator | 1. Low Cost
2. Simplicity 3. Minimal Maintenance Requirement |
1 Suitable for Small-Scale Use Only
2. May Cause Air Pollution 3. Unsteady Combustion and Ineffective Incineration |
| Single-Chamber Incinerator | 1. Simple Setup and Operation | 1. Does Not Meet Environmental Guidelines
2. Not Suitable for Heterogeneous Waste |
| Dual-Chamber Incinerator | 1. Can Perform Complete Combustion an Effective Incineration
2. Suitable for Thermal Treatment of Gaseous Effluents 3. Can Mitigate Air Pollution and Toxin Release 4. Good for Heterogeneous Waste |
1. May Require Significant Amount of Maintenance
2. Presence of Air-Control Systems may Cause Complexity |
| Fluidized Bed Incinerator | 1. Uniform Heat Transfer
2. Suitable for Particulate Waste and Other Types |
1. May Not be Effective for Large-Particle Waste, Liquid Waste, and Other Types
2. May have High Energy Demand, due to the Need for Continuous Supply of Preheated Air-Currents |
| Rotary Kiln Incinerator | 1. Effective Heat Transfer Mechanism
2. Suitable for Hazardous and Industrial Waste |
1. Relatively Complex Setup
2. High Maintenance Requirement 3. Relatively-High Energy Demand 4. Relatively-High Cost of Construction and Operation |
| Fixed Grate Incinerator | 1. Flexibility
2. Good for Odor and Smoke-Oil Mist Removal 3. Relatively Simple Setup 4. Can be Used to Treat a Broad Range of Waste Types |
1. Removal of Incineration Residue Must be Done Manually |
| Moving Grate Incinerator | 1. Effectiveness
2. Versatility 3. Very Suitable for Treatment of Municipal Solid Waste (MSW) 4. Incineration Residue is Easily Removed 5. May be Used Across a Wide Range of Temperature |
1. Relatively-High Capital and Operational Cost |
| Catalytic Combustion Incinerator | 1. Can be Used for Relatively Complex Cases like Solvent Abatement and Decomposition of VOCs
2. Suitable Where Complete Thermal Destruction is Required 3. Presence of Catalysts Increases Combustion Efficiency |
2. Relatively Complex and Expensive |
| Liquid Injection Incinerator | 1. Useful for Liquid Waste like Sewage Sludge and Industrial Effluent | 1. Relatively Complex Operation |
| Pyrolytic Incinerator | 1. Gaseous Emissions and Air Pollution are Minimized
2. Suitable for Waste-to-Energy Applications 3. Can be Used to Derive Specific Byproducts 4. Byproducts are Usually Valuable |
1. Is Not Suitable Where Complete Thermal Destruction is Required |
| Waste-Gas Flare Incinerator | 1. Good for Incineration Projects where Excessive Gaseous Byproducts are Released | 1. Is a Potential Cause of Greenhouse Emission and Air Pollution |
| Specialized Incinerator | 1. Suitable Where there are Very Specific Needs and Requirements | 1. Cannot be Used for A Wide Range of Applications |
Conclusion: Types of Incinerators, Factors for Classification
An incinerator or incineration plant, is a system or facility that is used to treat waste thermally by combustion.
The Types of Incinerators are;
- Drum Incinerator
- Single-Chamber Incinerator
- Dual-Chamber Incinerator
- Fluidized Bed Incinerator
- Rotary Kiln Incinerator
- Fixed Grate Incinerator
- Moving Grate Incinerator
- Catalytic Combustion Incinerator
- Liquid Injection Incinerator
- Pyrolytic Incinerator
- Waste-Gas Flare Incinerator
- Specialized Incinerator
Factors used to classify the types of incinerators include geometry, interior design, and purpose.
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