Incineration is one of the waste treatment technologies that involve the combustion of Municipal Solid Waste (MSW) without any pre-treatment (also called mass burning). Mass burning has been in practice in developed countries for more than 100 years. At present more than 600 mass burning plants are operating around the world.
Volume reduction of MSW for about 90% is possible with incineration plants, which can help in considerable land saving.
Only few countries in Asia have a long history of proper management of MSW using incineration power plants. Presently, in Singapore, 4 power plants of sizes ranging from 30 MW to 80 MW are in operation (for more than 30 years) and the government is processing the installation of new plants. A 2.5 MW plant is in operation in Phuket, Thailand.
The lower heating value of MSW varies considerably from country to country depending on several factors. In general, if the economic situation is better, then the heating value will be higher. For the mass burn facilities, the minimum calorific value requirement is 7 MJ/kg on an annual average basis.
The moisture content and percentage of combustibility are also important parameters in MSW mass burn technology. The impact of MSW scavenging on LHV should also be taken into account.
In MSW mass burn technology, there is no pre-treatment except the removal of visible bulk items. However, some of the wastes such as construction debris, earth, concrete, stones, chemical waste, explosive or highly flammable waste, carbon fibres, insulation materials, Polyvinyl Chloride (PVC) etc., are not suitable for mass burn. It is also advisable to separate biodegradable wastes from MSW to use in digesters so that biogas resulting from the digester can be used to generate power using gas engines.
MSW plants generally have limitations in the usage of steam cycle and also the plant design concept is different from biomass combustion system. Due to the level of complexity in design and lower demand for such plants in developing countries, there are only limited suppliers available in Asia. Though several suppliers may claim that they have the technical know-how, it is worthwhile to do a due-diligence on the supplier's capability. The equipment suppliers need more knowledge in combustion to burn MSW than to burn other kinds of fuels. The power plant should be designed with more flexibility and with a plenty of margins. Generally, the excess air requirement is high.
The investment cost and annual O&M costs for MSW based power plants are much higher than the biomass projects. The revenue generation from the sale of electricity alone is not sufficient to make the project commercially attractive. The major aspects which make the project commercially attractive are the tipping fee and CDM CER revenue, some few years back. The higher investment cost is mainly because of the use of high corrosion resistant materials for incinerator and complex environmental control systems. Also the money involved in the removal of SOx, NOx, dioxin, heavy metals, HCl and air born particulates, fly ash and bottom ash from mass burn power plants are high. The devices/processes commonly used for effective removal of pollutants include electrostatic precipitators, fabric filters, scrubber & lime injection system and activated carbon injection system.
With the use of modern technologies, it is also possible to minimise water pollution, odour and noise problems. It is also possible to recover ferrous metals from the ash, which provide additional revenue.
Implementing MSW projects are more time consuming than biomass power plants, as very careful preparatory work is needed for the incineration plants. Without proper preparation, the chances of failure of such plants are high. While we have visited several successful MSW plants that have been in operation for more than 30 years, we have also come across several failure plants which were sold as scrap. Hence, the project developers should pay adequate attention and do necessary preparatory work before implementing these projects. It may also be worthwhile to engage qualified experts to study all modern concepts and innovative technologies. But the technology selection should be done carefully.
The potential for incineration plants in developing countries is high. However several challenges also exist in the development of new projects. Among all MSW management systems, incineration to power is getting more and more popular in cities as it eliminates the need for land requirement in land filling. However, for the existing landfill sites that have been in operation for more than 10 years, landfill gas recovery and power generation using gas engine is practiced. Refused Derived Fuel (RDF) combustion, gasification and pyrolysis are also used as other options for power generation from MSW.
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