Sharing Date26 Mar, 2022
Together with the growth of human population in the planet, the increase in the consumption rate of natural resources and the generation of large amounts of waste become one of the biggest environmental problems of these days. The climate crisis, the negative effects of which we clearly feel in our daily lives, makes the environmentally-friendly management of generated wastes much more important day by day.
The waste hierarchy, created as a result of the studies carried out in cooperation with the academic and real sector in this field, prioritizes the methods of prevention of waste generation at source, reduction, reuse, recycling, energy recovery and disposal, respectively. Waste disposal, which stands at the bottom in this hierarchy (i.e. the least preferred option from an environmental point of view), should be carried out in an environmentally friendly way using the best available techniques for sure. The landfilling, biomethanation, composting, pyrolysis, gasification and incineration are the most common disposal methods. The types of wastes identified with respect to their physical and chemical conditions, the sources generated, their consumable potential and other similar characteristics, are accepted as the main indicators for the determination of the disposal method to be used.
The type of waste (according to the source generated; domestic, industrial, medical, agricultural and animal wastes, garden, construction and rubble wastes), waste content (percentage of carbon, hydrogen, sulfur, chlorine and oxygen), waste amount, hazard class, humidity rate, calorific value, organic/inorganic percentage, type of fuel to be used for combustion and the national/international emission standards[1] valid in the project area are the main design parameters of waste incineration systems.
The treatment of hazardous gases generated as a result of combustion process is provided by flue gas treatment systems that could be integrated onto the waste incineration system. These systems may consist of several stages, depending on the content of the flue gas. The main equipment are the loading unit and combustion chambers for the combustion part; and heat exchanger, bag filter and wet scrubber for the flue gas treatment part. The flow diagram of the integrated waste incineration system, which also shows other auxiliary equipment, is as in Figure 1.
Figure 1. Integrated Waste Incineration System Flow Diagram (1)
The Automatic Loading Unit designed depending on whether the waste is solid, liquid or gas provides transfer of the wastes to the Primary Combustion Chamber (PCC) without any human contact. In the PCC, the first combustion process is achieved at a temperature of between 800 and 1000 °C depending on the type of waste. As a result of this process, the ash and flue gas are generated in varying amounts depending on the organic/inorganic content of the waste. In the Secondary Combustion Chamber (SCC), the flue gas sourcing from PCC is combusted for the second time with extra air supply for a period of time given in the relevant standard at a temperature between 850 and 1200 °C. This process provides burning out of the most of hazardous organic substances that the flue gas contains. In both combustion chambers, the combustion processes are started with equipment called burners working with diesel, gasoline, natural gas or LPG, and in the following process, the wastes continue to burn with their own heat. The flue gas reached to high temperature values is cooled in the Heat Exchanger with water, oil or air before transferring to flue gas treatment system in order to prevent any damage to the system equipment. The dry, wet or both types of flue gas treatment systems could be used to release the flue gas cooled in the Heat Exchanger to the atmosphere in accordance with the emission limit values given in the valid standards in project region. While dry type flue gas treatment systems are mainly used for the removal of particulate matter, wet systems provide efficient treatment of pollutive acidic gases in the flue gas.
With integrated systems in which waste incineration and flue gas treatment systems are used together, wastes are disposed in a rate of 95% by volume and 75% by mass. These systems provide that hazardous materials are destroyed without causing any harmful emissions, as well as significant reduction in the costs of waste management activities such as waste storage. The ash generated as a result of the combustion of organic materials could be used as a by-product in processes such as cement and asphalt production. The hot water, steam or boiling oil generated as a result of flue gas cooling process can be used for heat and electrical energy generation depending on the waste type and capacity. Another important environmental problem such as the emission of bad odor encountered in other disposal methods is out of the question for these systems.
The disposal methods should also be evaluated among themselves considering the current requirements for the wastes which are clearly deemed to be impossible to manage with methods placed at the top of the waste hierarchy. Although the destruction of unnecessary materials by burning is a primitive method applied since ancient times, the efficient and environmentally friendly outputs could be achieved with the integrated waste incineration systems designed in the light of the latest developments in technology. Although these systems are more commonly preferred in developing and underdeveloped countries, they are also still seen as an important alternative by developed countries.
Reference
1) Santes Incinerator (2015); www.santes.com.tr; Retrieved from: http://santes.elizyazilim.net/uploads/santes-catalogue.pdf
Footnote
1) EU 76/2000/E C, ABPR, EPA, other international standards or national standards included in local regulations.
