Incineration Meaning, Types, Conditions, Comparison
Incineration is the burning of a substance or material in the presence of oxygen, and under controlled conditions.
This article discusses incineration based on the following outline;
-Incineration Meaning: 7 Ways to Define Incineration
-Overview of the Incineration Process
-Incineration and Open Burning: A Comparison
-Incineration Plant: Types of Incinerators
Incineration Meaning: 7 Ways to Define Incineration
Incineration is simply the process of burning a material.
There are various materials which may be burnt during incineration, These materials can be used to define the concept, as follows;
Incineration is the burning of waste, biomass or other inorganic and organic materials under controlled conditions, in the presence of oxygen.
With regards to waste, incineration is also relevant as a method of producing energy from waste, as expressed below;
Incineration is a waste-to-energy method which involves the combustion of waste under controlled conditions, to produce renewable energy in the form of heat, which may in turn be used to generate electricity.
Another perspective that can be employed to define incineration is the underlying mechanism of the process. This is conveyed in the following definition;
Incineration is an engineered process whereby materials are made to undergo combustion and thermal decomposition in the presence of oxygen, to produce heat and other byproducts.
A notable area of importance of incineration is with regards to waste management and addressing environmental degradation caused by waste;
Incineration is a waste management method where non-recyclable wastes are treated by thermal method through combustion in the presence of oxygen.
With regards to waste management, the definition of incineration can include the types of waste which can be treated using this method;
Incineration is the burning of various types of waste like municipal solid waste (MSW), medical waste, organic waste, E-waste, and other forms of hazardous waste, resulting in their thermal decomposition, with the release of heat energy.
Lastly, incineration can be defined on the basis of the reactions and products involved;
Incineration is the combustion, oxidation and thermal decomposition of materials to produce carbon dioxide (CO2), water vapor, flue gases, ash, and other products of incomplete combustion.
The main function of incineration is thermal decomposition of the substance. Heat energy is usually a byproduct of this decomposition process, alongside other products like ash and gaseous effluents.
Overview of the Incineration Process
Incineration is the most common waste-to-energy method, because of its simplicity.
The steps in the incineration process are heating, combustion, oxidation, thermal decomposition, and destruction. These are discussed individually below;
1). Heating
Heating is the first step in the incineration process.
It basically refers to the application of heat directly to a material.
Heating is essential during incineration as it leads to subsequent decomposition and destruction of the material.
2). Combustion
Combustion occurs as a result of heating during incineration.
Because the material is exposed to air, it ignites and burns. This stage is what differentiates incineration from other waste-to-energy methods like gasification and pyrolysis.
Combustion is also what causes the eventual destruction (rather than thermal conversion) of the material that is undergoing incineration.
3). Oxidation
Combustion is itself a type of oxidation reaction, during which the molecules of a compound are combined chemically with oxygen, at high temperature [7].
Therefore as a result of combustion, the material which is undergoing incineration becomes oxidized.
4). Thermal Decomposition
Combustion (high-temperature oxidation) causes thermal decomposition of a material.
This basically is the breakdown of the chemical compounds that make up the material/substance, under the influence of temperature.
Thermal decomposition results in simpler chemical compounds like carbon dioxide (CO2) and water vapor (H2O).
5). Destruction
The final stage of incineration is the thermal destruction of a material or substance.
This is different from thermal conversion which occurs in other waste management/waste-to-energy methods like pyrolysis and gasification.
Thermal destruction occurs because incineration is not a strictly-controlled process. Other methods usually include measures that limit the amount of heat or oxygen that is allowed to come into contact with a material.
As a result of thermal destruction, byproducts like char and gaseous effluents, are produced in large quantities during incineration.
Incineration and Open Burning: A Comparison
Incineration differs from open burning by being a controlled process. Incinerators may include equipment that regulate the heating and combustion temperature, gas production, and other parameters involved in the incineration process.
The following table outlines the basic differences between incineration and open burning;
| Incineration | Open Burning |
| Is usually a controlled process | Is usually allowed to occur spontaneously |
| Is designed to achieve complete combustion and thermal destruction | Is not designed to achieve complete combustion due to its spontaneity |
| Takes place in an incinerator under engineered and pre-designed conditions | May take place in any open space |
| Generally produces less toxic effluents | More toxic and hazardous effluents are produced |
| May include energy recovery equipment to collect heat (for domestic heating and electricity generation) as well as other combustion products | Does not include any energy recovery equipment |
Incineration Temperature
Incineration may occur across a wide range of temperature conditions, with an average of 500-1,200°C.
The temperature of incineration depends on the nature of material undergoing incineration, and the characteristics or external and internal conditions of the incinerator.
Types of Incineration
Types of incineration are limited-air, excess-air, steam-based, power-based, and cogeneration-based incineration.
These four types are classified on their purpose and mode of control, as elaborated below;
Incineration Types Based on Purpose
1). Steam-based Incineration
As the name implies, steam-based incineration is focused primarily on the production of steam.
Steam is itself a valuable commodity which is used for various industrial applications [2].
In order to produce steam, the heat energy from incineration is applied to water, raising its temperature to the boiling point.
This water is converted to steam, which may then be transmitted through steam lines, to the point of use. Possible applications include space heating and cooling, as well as manufacturing.
2). Power-based Incineration
Power-based incineration is as a waste-to-energy method whereby waste is burnt in the presence of oxygen, for the sole purpose of electricity generation.
This is basically an extended, elaborate form of the steam-based incineration. It includes equipment like a turbine generator, that convert the steam to mechanical energy, which is used to produce electricity through the principle of electromagnetism.
Power-based incineration is arguably the most important type, due to the versatile application of electric power.
However, it is also one of the most complicated and expensive types of incineration.
The need for a constant supply of steam makes it necessary to regulate the temperature and pressure of the system in a strict and consistent manner. This demands more sophisticated technology, which implies more expenditure.
Also, other fuels like natural gas may be used to augment the waste, so that sufficient heat energy and steam can be produced.
3). Cogeneration-based Incineration
Cogeneration-based incineration, produces both heat energy (stored in the form steam) and electricity.
As the name implies, it functions based on cogeneration (CHP) technology, and is designed to collect heat (steam) that has not been used to generate electricity.
Due to its energy-conservative design, the cogeneration-based incineration process achieves a relatively-high level of energy efficiency.
Similarly, a cogeneration-based incinerator acts as an energy management system, by minimizing energy losses in an effective manner. As a result of this, it s arguable that, although cogeneration-based incineration is relatively complex, it is the most economic form of incineration.
Incineration Types Based on Mode of Control
1). Limited-Air Incineration
Limited-air incineration is a type of incineration that involves the use of a sealed incinerator to control the amount of air or oxygen that comes into contact with the substrate (waste/fuel in the incinerator).
Unlike conventional incineration, this type is carried out in a similar manner to pyrolysis, which is a process of thermal decomposition in the absence of air/oxygen [3].
Limited-air incineration is needed in specific cases, such as where the substrate is highly toxic or volatile, and where certain products of combustion are to be collected.
2). Excess-Air Incineration
Excess-air incineration is more similar to open air burning, in that there is no limit to the amount of oxygen which is allows to enter the incinerator.
This means that oxidation occurs effectively alongside combustion in an excess-air incinerator.
The advantage of this is a relatively-simple and effective thermal-destruction process for substrate material. However, it usually involves larger emissions of greenhouse gases and other toxins that can degrade the air quality, cause environmental degradation, and health problems.
Incineration Plant: Types of Incinerators
An incineration plant, also known as an incinerator, is a waste treatment vessel or facility in which waste is treated through a thermal process of combustion and oxidation, ultimately leading to the destruction of the waste and the production of gaseous and solid byproducts.
When the heat energy produced from burning waste in an incineration plant is collected and used, the waste has served as a fuel and a source of renewable energy.
In such cases, the incinerator can be called a waste-to-energy facility.
There are numerous types of incinerators, including rotary-kiln, fixed grate, moving grate, liquid injection, multiple hearth, fluidized bed and catalytic combustion incinerators.
Among the numerous options, the three main types of incinerators are fluidized bed, liquid injection and rotary-kiln incinerators. These types are discussed as follows;
1). Fluidized-Bed Incinerator/Incineration Plant
The fluidized bed incinerator is designed with a bed of sand or similar material, through which a current of pressurized air is passed.
This air current is usually preheated [1], and its presence in the incinerator provides an advantage of effective and seamless heat transfer from the supply system to the waste material or any other substrate in the incinerator.
Because of its heat transfer efficiency, the fluidized-bed incinerator is capable of treating different phases of materials including solid and liquid waste. It is used in the treatment of municipal sludge [4].
2). Liquid-Injection Incinerator/Incineration Plant
Liquid-injection incinerator is designed to treat waste that occurs in aqueous and non-aqueous forms.
These include sludges and slurries, which may also contain some solid materials.
This type of incinerator is usually equipped with a fixed bed that transfers heat efficiently to the liquid waste.
It derives its name from the fact that the liquid waste is usually introduced into the system by injection. The liquid injection is particularly useful for treating hazardous waste such as industrial effluents and radioactive liquid waste.
3). Rotary-Kiln Incinerator/Incineration Plant
A rotary-kiln incinerator is an inclined cylindrical tube which is internally lined with refractory materials, and which rotates on its axis [6].
The role of the cylindrical tube is to act as a heating vessel into which the waste is introduced. By rotating, the tube provides a mechanism for efficient heat transfer and thermal decomposition.
To achieve these advantages, the kiln often rotates at a slow pace, and may have high temperatures of up to 850°C [5].
Conclusion
Incineration is a method of waste management and waste-to-energy conversion, whereby materials are made to undergo combustion and thermal destruction in the presence of oxygen.
The five steps in the process of incineration are;
- Heating
- Combustion
- Oxidation
- Thermal Decomposition
- Destruction
Types of incineration are;
- Steam-based Incineration
- Power-based Incineration
- Cogeneration-based Incineration
- Limited-Air Incineration
- Excess-Air Incineration
An incinerator or incineration plant, is a system that is designed to carry out incineration.
The three main types of incinerators are;
- Fluidized-Bed Incinerator
- Liquid-Injection Incinerator
- Rotary-Kiln Incinerator
References
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2). Einstein, D.; Worrell, E.; Khrushch, M. (2001). “Steam systems in industry: Energy use and energy efficiency improvement potentials.” Available at: https://www.researchgate.net/publication/255271068_Steam_systems_in_industry_Energy_use_and_energy_efficiency_improvement_potentials. (Accessed 29 April 2022).
3). Ibrahim, H. A. (2020). “Introductory Chapter: Pyrolysis”, in H. A. H. Ibrahim (ed.), Recent Advances in Pyrolysis, IntechOpen, London. Available at: https://doi.org/10.5772/intechopen.90366. (Accessed 29 April 2022).
4). Kowarska, B.; Baron, J.; Kandefer, S.; Zukowski, W. (2013). “Incineration of Municipal Sewage Sludge in a Fluidized Bed Reactor.” Engineering 5(1A):125-134. Available at: https://doi.org/10.4236/eng.2013.51A018. (Accessed 29 April 2022).
5). Liu, S.; Wang, F.; Wu, J. (2020). “Parameter design of rotary kiln incinerator and application analysis in engineering cases.” IOP Conference Series Earth and Environmental Science 514(3):032047. Available at: https://doi.org/10.1088/1755-1315/514/3/032047. (Accessed 29 April 2022).
6). Lombardi, F.; Lategano, E.; Cordiner, S.; Torretta, V. (2013). “Waste incineration in rotary kilns: A new simulation combustion tool to support design and technical change.” Waste Manag Res. 2013 Jul;31(7):739-50. Available at: https://doi.org/10.1177/0734242X13484187. (Accessed 29 April 2022).
7). Wilson, B.; Williams, N.; Liss, B. (2013). “A Comparative Assessment of Commercial Technologies for Conversion of Solid Waste to Energy.” Available at: https://www.researchgate.net/publication/280080635_A_Comparative_Assessment_of_Commercial_Technologies_for_Conversion_of_Solid_Waste_to_Energy. (Accessed 29 April 2022).
