Thermal Waste Treatment

Thermal waste treatment technologies / methods

Thermal waste treatment refers to the processes that use heat to treat waste materials. Following are some of the most commonly used thermal waste treatment techniques:

• Incineration, this approach involves the combustion of waste material in the presence of oxygen. Incineration as a thermal treatment method is commonly used as a means of recovering energy for electricity or heating. This approach has several advantages.; it quickly reduces waste volume, lessens transportation costs, and decreases harmful greenhouse gas emissions.
• Gasification and pyrolysis are two similar methods, both of which decompose organic waste materials by exposing waste to low amounts of oxygen and very high temperatures. Pyrolysis uses no oxygen while gasification allows a low amount of oxygen in the process. Gasification is more advantageous as it allows the burning process to recover energy without causing air pollution.
• Open burning is a legacy thermal waste treatment that is environmentally harmful. The incinerators used in such a process have no pollution control devices. They release substances such as hexachlorobenzene, dioxins, carbon monoxide, particulate matter, volatile organic compounds, polycyclic aromatic compounds, and ash.

Waste incineration

Incineration is one of the most common waste treatments. This approach involves the combustion of waste material in the presence of oxygen.

Waste incineration involves converting waste materials into ash, flue gas, and heat. The ash mostly consists of non-organic components of waste and can be in the shape of solid lumps or particulates carried by the flue gas. The flue gases are to be cleaned of particulate and gaseous contaminants before being released into the air.

In waste incineration, the most common technique is called “mass burn.” This general process consists of 5 steps.

• Waste preparation: Oversized items are removed and certain recyclables like metals are recovered.
• Combustion: Waste is burned in an oxygenated single combustion chamber.
• Energy recovery: The gases released during combustion are cooled with water.
• Environmental control: The cooled gas is treated by scrubbers, precipitators, and filters to remove pollutants.
• Environmental release: The treated gas is released into the atmosphere.

Advantages and disadvantages of waste incineration

Incinerators also have their downsides. Some of the most common advantages and disadvantages are listed below.

• Advantages
  • Decreased quantity of waste
  • Efficient waste management
  • Production of heat and power
  • Reduction of pollution
  • Saves on transportation of waste
  • Prevents the production of methane gas
• Disadvantages
  • Expensive
  • Pollutes the environment
  • Harms public health

Pyrolysis

Pyrolysis is the process of heating organic material, such as biomass, in the absence of oxygen. Because no oxygen is present the material does not combust but the chemical compounds, such as cellulose and lignin, that make up that material thermally decompose into combustible gases and charcoal. Most of these combustible gases can be condensed into a combustible liquid, called pyrolysis oil.

The pyrolysis process is used heavily in the chemical industry, for example, to produce ethylene, many forms of carbon, and other chemicals from petroleum, coal, and even wood, to produce coke from coal. It is also used in the conversion of natural gas into non-polluting hydrogen gas and non-polluting solid carbon char, initiating production in industrial volume.

Variables that can alter the pyrolysis process

• Treated material composition: each of the major constituents of biomass and waste feature different temperatures of thermal decomposition.
• Temperature of the process: Higher temperatures of pyrolysis provide a greater quantity of non-condensable gases, while lower temperatures favor the production of high-quality solid products.
• Residence time of material in the pyrolysis chamber: influences the degree of thermal conversion of received solid product as well as the residence time of the vapor.
• Particle size and physical structure: influences the speed at which material is subjected to pyrolysis.

Gasification

Gasification is a process that converts biomass- or fossil fuel-based materials into gases. This is achieved by reacting the material at high temperatures without combustion, via controlling the amount of oxygen and/or steam present in the reaction. An advantage of gasification is that syngas can be more efficient than direct combustion of the original feedstock material because it can be combusted at higher temperatures.

Gasification is similar to combustion but it’s different in the amount of oxygen used in the process. Combustion uses an abundance of oxygen to produce heat and light by burning. Gasification uses only a tiny amount of oxygen, which is combined with steam and cooked under intense pressure.

Plasma gasification

Plasma is a very high temperature, highly ionized gas capable of conducting electrical current. Examples of plasma in nature include lightning and gas at the surface of the sun.

Plasma gasification is a waste-treatment technology that uses a combination of electricity and high temperatures to turn municipal waste into usable by-products without combustion. Although the technology is sometimes confused with incinerating, plasma gasification does not combust the waste as incinerators do. Instead, it converts the organic waste into a gas that still contains all its chemical and heat energy and converts the inorganic waste into an inert vitrified glass called slag. The process can reduce the volume of waste sent to landfills and generate electricity.

Waste drying

Waste drying is the drying of materials that have been contaminated with hazardous chemical waste. This waste must be handled, stored, and disposed of properly. Dry waste is comprised of a mix of timber, metals, plastics, cardboard, and paper, as well as small amounts of concrete, bricks, and rubble.

Examples of dry waste

• Contaminated soils
• Extremely hazardous waste containers
• Debris that is contaminated
• Dried chemicals that are in scrapable amounts

Waste drying benefits

• Considerably reduce transport costs
• To transform a final waste aimed to a landfill into a waste-to-energy process
• Households refuse transformation into a solid recovered fuel
• Dried grains commercialization for animal feed
• Coproducts value from the forest industry into densified sticks, granules
• To control the activities environmental impact