WASTE INCINERATION

1.            SCIENTIFIC AND TECHNICAL INFORMATION

1.1        Basic Principles of Waste Incineration

Incineration is the oxidative degradation of waste at high temperatures, which results in a rapid, exothermic reaction. To put it simply, it means the burning of waste in order to destroy or decrease waste volume, to produce energy from waste or dispose of medical and hazardous waste. Although the main advantage of the process is the reduction achieved in the volume of waste, it also has its obvious disadvantages. Incinerators can be extremely expensive unless some kind of energy recovery technique is applied. Also old, out-of-date facilities can release fly ash, noxious gases, and chemical contaminants into the air. Though this latter problem is overcome with the development of new and efficient techniques for scrubbing pollutants from incinerator stacks, a strong and persistent public opposition to waste incineration still persists.

   

 

As defined by environmental standards, waste-to-energy technology is to be odour-free, smoke-free and dust-free, suitable for burning many highly flammable, volatile, toxic and infectious wastes, which should not be landfilled without special treatment. It removes toxins and minimises the volume of waste for final disposal by about 80-90%. Most importantly producing energy from waste not only reduces the impacts of landfill, but also utilises a resource that would otherwise be disposed.

Indeed more than half of the waste incinerated consists of organic materials, such as wood, paper and cardboard. Using organic material to generate electricity displaces fossil fuels such as natural gas, coal and oil, contributing to a smaller increase of the greenhouse effect. In fact, the amount of CO₂ released during the incineration of organic materials is the same as that taken up by trees and crops grown to produce them, thus keeping the amount of atmospheric CO₂ in balance.

When waste is used to produce energy, it is commonly referred to as a “waste-to-energy” or “energy from waste” technology. It means that waste that piled up is not simply burnt, but put to maximum use through heat recovery. The combustion of waste releases a considerable amount of heat, which is then used to generate electricity. Besides incineration there are three other ways to produce energy from waste: selected wastes can be converted into fuel, methane released by landfills can be collected and burnt, or biogas (basically methane) can be directly produced through the biological conversion of waste, i.e. by controlled anaerobic digestion. Fuel derived from waste can be then used either as motor fuel or for heat, steam or electricity generation.

Most of the waste-to-energy plants are connected to the national grid, supplying millions of households. Though its worldwide acceptance is generally on the increase, incineration itself still has a controversial standing. Sometimes it poses fierce debate and raises opposition on the part of local advocacy groups. It is true that before the era of recycling, waste prevention and emission control, incinerators released a considerable amount of air pollutants and had not much concern for ash residue treatment. Generally it was the result of feeding incinerators with a mixture of unprocessed and heterogeneous waste stream and/or uncontrolled operation. Accordingly waste often underwent incomplete combustion. But waste incineration technology and emission control have improved significantly over the recent past, therefore the environmental risks that used to be associated with old incinerators are minimised.

Modern technology enables waste incineration to be considered a clean and renewable source of energy. Therefore it represents an ecologically viable option for the treatment of waste that cannot be avoided or directly recycled. Incineration has a number of advantages, particularly over landfilling. As an example, energy from waste yields five times more useful energy per tonne than energy recovery from landfills. Although incineration plants use about 20% of the electricity generated from wastes themselves, combustion heat can be further exploited in the production of distilled water or in district heating schemes. It may also be used for drying sewage sludge and heating greenhouses.