Incineration is the main waste-to-energy form of treatment. It is a treatment technology involving destruction of solid waste by controlled burning at high temperatures. It is accompanied by the release of heat. This heat from combustion can be converted into energy. Incineration is a high-quality treatment for Municipal Solid Waste (MSW), very useful in big or crowded cities, because it reduces the quantity and volume of waste to be land filled. It can be localised in an urbanised zone, and offers the opportunity of recovering energy. However, it should be taken into account that the economic investment needed is high. The environmental conditions of the incineration process must be very precise to make it environmentally safe. The larger portion of the investment required is due to environmental measures such as emissions control. When choosing incineration as an alternative, the following issues should be considered: volume/quantity of waste produced, heat of combustion of waste, site location, dimensions of the facility, operation and maintenance costs and investment.
In most of the countries both energy systems and waste management systems are under change. The changes are largely driven by environmental considerations and one driving force is the threat of global climate change. When making new strategic decisions related to energy system and waste management systems it is therefore of importance to consider the environmental implications.Municipal Solid Waste (MSW) contains organic as well as inorganic matter. Part of organic matter is more as compared to inorganic matter.
The latent energy present in its organic fraction is recovered for gainful utilisation through adoption of suitable Waste Processing and Treatment technologies. The recovery of energy from solid wastes also offers a few additional benefits which are as follows:
(i) The total quantity of solid waste gets reduced up to 90%, depending upon the waste composition and the adopted technology;
(ii) (ii) Demand for land, which is already scarce in cities, for land filling is reduced; (iii) The cost of transportation of waste to far-away landfill sites also gets reduced; and (iv) Reduction in environmental pollution.
It is, therefore, only logical that, while every effort should be made in the first place to minimise generation of waste materials and to recycle and reuse them to the extent feasible, the option of Energy Recovery from Wastes be also duly examined. Wherever feasible, this option should be incorporated in the over-all scheme of Waste Management.
A waste hierarchy is used in waste policy making and is often suggested. Different versions of the hierarchy exist but in most of the cases the following order suggests: 1. Reduce the quantity of waste 2. Reuse 3. Recycle the materials 4. Incinerate with heat recovery 5. Landfill of inert ash
The first priority, to reduce the quantity or volume of waste, which is generally accepted. However, the remaining waste needs to be taken care of as efficiently as possible. The hierarchy after the top priority is often contested and discussions on waste policy are in many countries intense.
Volume reduction of residues
Loading of waste into the process
Thermal treatment of the waste
Energy recovery and conversion
Emissions monitoring and control
Waste water control and treatment (e.g. from site drainage, flue-gas treatment, storage)
Ash/bottom ash management and treatment (arising from the combustion stage.
The purpose of Incineration to combust solid wastes to reduce their volume to about one tenth, without producing offensive gases and ashes.
Incineration is the process of direct controlled burning of waste in the presence of oxygen at temperatures of about 8000C and above, liberating heat energy, gases and inert ash. Net energy yield depends upon the density and composition of the waste. Relative percentage of moisture and inert materials, which add to the heat loss; ignition temperature; size and shape of the constituents; design of the combustion system, etc. In practice, about 65 to 80% of the energy content of the organic matter can be recovered as heat energy, which can be utilised either for direct thermal applications, or for producing power with the help of steam turbine-generators. The combustion temperature of conventional incinerators fuelled only by wastes are about 7600C in the furnace and in excess of 8700C in the secondary combustion chamber. These temperature are needed to avoid odour due to incomplete combustion but are insufficient to burn or even melt some of the inorganic contents such as glass. To avoid the deficiencies of conventional incinerators, some modern incinerators utilise higher temperature of up to 16500C using auxiliary fuel. These reduce waste volume by nearly 97% and convert some inorganic contents such as metal and glass to inert ash.
FLOW CHART OF INCINERATION SYSYTEM
Wastes burned solely for volume reduction may not need any supplementary fuel except for start-up. When the objective is steam production, auxiliary fuel may have to be used with the pulverized refuse, because of the variable energy content of the waste or in the event that the quantity of waste available is insufficient. While Incineration is extensively used as an important method of waste disposal, it is associated with some polluting discharges which are of environmental concern, although in varying degrees of severity. These can fortunately be effectively controlled by installing suitable pollution control devices and by suitable furnace construction and control of the combustion process.
The basic operational steps of a waste incineration plant may include the following: Reception of incoming waste • Storage of waste and raw materials
• Pre-treatment of waste
• Loading of waste into the process
• Thermal treatment of the waste
• Energy recovery and conversion
• Flue-gas cleaning
• Flue-gas cleaning residue management
• Flue-gas discharge
• Emissions monitoring and control
• Waste water control and treatment (e.g. from site drainage, flue-gas treatment, storage)
• Ash/bottom ash management and treatment (arising from the combustion stage)
• Solid residue discharge/disposal.
There are many options for MSW incineration plant technology. The range of equipment varies from experimental to well-proven, though only the well-proven are recommended. Development problems with new technology are complicated and costly to solve, as developing countries lack the internal technical expertise to overcome them. Such problems could cause the entire project to fail.
Based on the intended application, incineration plant equipment may be grouped in four main categories:
B. Combustion system
C. Energy recovery
D. Flue gas cleaning
Incineration is an efficient way to reduce the waste volume and demand for landfill space.
Incineration plants can be located close to the centre of gravity of waste generation, thus reducing the cost of waste transportation.
Using the ash from MSW incinerators for environmentally appropriate construction not only provides a low cost aggregate but further reduces the need for landfill capacity.
The slag quality should be verified before it is used.
Energy can be recovered for heat or power consumption.
Incineration provides the best way to eliminate methane gas emissions from waste management processes.
Furthermore, energy from waste projects provides a substitute for fossil fuel combustion.
These are two ways incineration helps reduce greenhouse gas emissions.
One of the most attractive features of the incineration process is that it can be used to reduce the original volume of combustibles by 80 to 95%. Air pollution control remains a major problem in the implementation of incineration of solid waste disposal.
Not all waste can be burned (there will still be landfill)
Release hundred of toxic chemicals into the atmosphere .
Disposal of ash (the toxic substances are more concentrated in the ash)
Highly related to economic condition.
Incineration plants involves the heavy investment & operating cost.
The complexity of incineration requires skilled staff.