Moving Grate Incineration: Preferred WTE Technology

moving-grate-incinerationIncineration is the most popular waste treatment method that transforms waste materials into useful energy. The incineration process converts waste into ash, flue gas, and heat. The type of thermal WTE technology most commonly used worldwide for municipal solid waste is the moving grate incineration. These moving grate incinerators are even sometimes referred to as as the Municipal Solid Waste Incinerators (MSWIs). As of August 2013, of more than 1000 of 1200 Waste-to-Energy plants (among 40 different countries) there is no pre-treatment of the MSW before it is combusted using a moving grate. The hot combustion gases are commonly used in boilers to create steam that can be utilized for electricity production. The excess energy that can’t be used for electricity can possibly be used for industrial purposes, such as desalination or district heating/cooling

Benefits of Moving Grate

The moving grate incineration technology is lenient in that it doesn’t need prior MSW sorting or shredding and can accommodate large quantities and variations of MSW composition and calorific value. With over 100 years of operation experience, the moving grate incineration system has a long track record of operation for mixed MSW treatment. Between 2003 and 2011, it was reported that at least 106 moving grate incineration plants were built worldwide for MSW treatment. Currently, it is the main thermal treatment used for mixed MSW.

Compared to other thermal treatment technologies, the unit capacity and plant capacity of the moving grate incineration system is the highest, ranging from 10 to 920 tpd and 20 to 4,300 tpd. This system is able to operate 8,000 hours per year with one scheduled stop for inspection and maintenance of a duration of roughly one month. Today, the moving grate incineration system is the only treatment type which has been proven to be capable of treating over 3,000 tpd of mixed MSW without requiring any pretreatment steps. Being composed of six lines of furnace, one of the world’s largest moving grate incineration plants has a capacity of 4,300 tpd and was installed in Singapore by Mitsubishi in 2000

Working Principle

Moving-grate incineration requires that the grate be able to move the waste from the combustion chamber to allow for an effective and complete combustion. A single incineration plant is able to process thirty-five metric tons of waste per hour of treatment.

The MSW for a moving grate incinerator does not require pretreatment. For this reason, it is easier to process large variations and quantities. Most of these incineration plants have hydraulic feeders to feed as-received MSW to the combustion chamber (a moving grate that burns the material), a boiler to recover heat, an air pollution control system to clean toxins in the flus gas, and discharge units for the fly ash. The air or water-cooled moving grate is the central piece of the process and is made of special alloys that resist the high temperature and avoid erosion and corrosion.

The waste is first dried on the grate and then burnt at a high temperature (850 to 950 degrees C) accompanied with a supply of air. With a crane, the waste itself is emptied into an opening in the grate. The waste then moves towards the ash pit and it is then treated with water, cleaning the ash out. Air then flows through the waste, cooling the grate. Sometimes grates can also be cooled with water instead. Air gets blown through the boiler once more (but faster this time) to complete the burning of the flue gases to improve the mixing and excess of oxygen.

Suitability for Developing Nations

For lower income and developing countries with overflowing landfills, the moving grate incinerator seems suitable and efficient. Moving grate incineration is the most efficient technology for a large-scale mixed MSW treatment because it is the only thermal technology that has been able to treat over 3,000 tons of mixed MSW per day. It also seems to be considerably cheaper than conventional technologies.

Compared to other types of Waste-to-Energy technologies, this type of system also shows the highest ability to handle variation of MSW characteristics. As for the other incineration technologies like gasification and pyrolysis technologies, these are either limited in small-scale, limited in material for industrial/hazardous waste treatment, requiring preprocessing of mixed MSW before feeding, which make them not suitable for large-scale mixed MSW treatment.

Conclusion

For the reduction of significant waste volume, treatment using a moving grate incinerator with energy recovery is the most commonly used form of waste-to-energy (WTE) technology. The moving grate’s ability to treat significant volumes of waste efficiently, while not requiring pre-treatment or sorting is a major advantage that makes this suitable for developing countries. This technology could provide many other benefits to such nations. Implementing moving grate incinerators is most suitable for developing nations because not only will it reduce waste volume, but it would also reduce the demand for landfills, and could recover energy for electricity.

References

 “A Rapidly Emerging WTE Technology: Circulating Fluid Bed Combustion”. Huang, Qunxing, Yong Chi1, and Nickolas J. Themelis. Proceedings of International Thermal Treatment Technologies (IT3), San Antonio, TX, October 2013. Columbia University. Available: http://www.seas.columbia.edu/earth/wtert/sofos/Rapid_Emerging_Tech_CFB.pdf accessed on 29 March 2016.
“Incineration.” Waste Management Resources. Waste Management Resources. Available: http://www.wrfound.org.uk/articles/incineration.html accessed on 29 March 2016.
Kamuk, Bettina, and Jørgen Haukohl. ISWA Guidelines: Waste to Energy in Low and Middle Income Countries. Rep. International Solid Waste Association, 2013. Print.
“Municipal Solid Waste Management and Waste-to-Energy in the United States, China and Japan.” Themelis, Nickolas J., and Charles Mussche. 2nd International Academic Symposium on Enhanced Landfill Mining, Houthalen and Helchteren, Belgium, 4-16 October 2013.  Enhanced Landfill Mining. Columbia University. Available: http://elfm.eu/Uploads/ELFM/FILE_73D907E9-8225-4B93-91F8-10F71F59B793.PDF accessed on 29 March 2016.
“Review of MSW Thermal Treatment Tecnologies.” Lai, K.C.K., I.M.C. Lo, and T.T.Z. Liu. Proceedings of the International Conference on Solid Waste 2011- Moving Towards Sustainable Resource Management, Hong Kong SAR, P.R. China, 2 – 6 May 2011. Hong Kong SAR, P.R. China. 2011. 317-321. Available: http://www.iswa.org/uploads/tx_iswaknowledgebase/10_Thermal_Technology.pdf. accessed on 14 April 2016.
UN-HABITAT, 2010. Collection of Municipal Solid Waste in Developing Countries. United Nations Human Settlements Programme (UN-HABITAT), Nairobi. Available:
http://www.eawag.ch/fileadmin/Domain1/Abteilungen/sandec/E-Learning/Moocs/Solid_Waste/W1/Collection_MSW_2010.pdf.
World Bank, 2012. What a Waste: A Global Review of Solid Waste Management. Urban Development Series Knowledge Papers. Available: http://documents.worldbank.org/curated/en/2012/03/16537275/waste-global-review-solid-wastemanagement. accessed on 14 April 2016.

About Rachael Lew

Rachael Lew is a student in her last year of completing her Bachelor’s degree with a focus in Archaeology and Environmental Science at Willamette University (USA). She is particularly interested in Environmental Sustainable Development and Geographic Information Systems and hopes to continue her studies and pursue these in a graduate degree. Lew has rich experience in blogging, and working at the university paper, The Collegian. She is also currently assisting with research for Willamette Partnership, a non-profit organization that works to create solutions for conservation. Rachael is associated with BioEnergy Consult as a research intern.
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2 Responses to Moving Grate Incineration: Preferred WTE Technology

  1. Paul says:

    How can incineration ever be acceptable. It destroys the very product collected via the Circular Economy in terms of waste and condemns it to a single process that destroys all possibility of ever being re-invented in another form.

    In a similar way you ignore the point that in these days where there are no Gate Fees for Treatment (and there should not be as theses are unecessary) and wheen there are noi needs for any subsidies to build these the costs of incineration are EXORBIDENTLY HIGH and TOO COSTLY to build for the limited financial returns. We read that such Gate Fees are often shown as beinf around US$ 80 to !00 per tonne input and that for a projected waste stream of 800,000 tonnes per year the Caoital Costs are enormous at over $500 million. Now when – even in Columbia University’s own reports on incineration where it is said that when the water or moisture content is around 40 to 45% – and it can be higher in Asia often reaching 60% – of the input stream the reality of the process is totally faulted. You cannot generate energy as electricity from burning water. Then you have to deal with te Carcinogenic and Toxic residues at around 30% of the input stream by mass and these need carefully managing and interring. Such residues are conveniently ignored by you here but are still an issue. With toxic residues costing over $1800-00 per tonne to inter for over 100 years this is an issue you have totally ignored. So even in your own repoorts and documents written fairly recently you remind us that incineration is not then favoured.

    You must be consistent with your thesis and documents since if anyone were to lay out reall questions about your work then there cannot be an aceptable use of incineration.

    We hear that it is more beneficial to recapture the organic fraction within the the MSW and convert this to the Renewable Fuels/Energies. Here we are advised that a project for dealing with 600,000 tonnes per year of such organic material could be treated for less than $270 million and deliver renewable fuels worth over $140 Million a year for use in transport as well as make Electricity worth a further $30 million a year. By any comparison you cannot better that with incineration.

    ON this basis you can now see that the Capital Costs can be repaid by revenue streams within 3 years *maybe 4 years at most) and that means very impressive benefits. Taken further still, with the fuel equivalent of around 1.5 Million barrels of oil not used and thus not imported in to a country that additional equivalent reduction in imports is still to be added. Thus for countries in ASia (including China as you mentioned it) your comments are faulted.

  2. Patrick says:

    Exactly my opinions.

    China is making a huge and costly mistake ever embarking on this route.

    I hear that they are looking at a 5000 tonne per day plant that will cost almost RNB5Billion and that is for gasification which does not work either. Surely making the renewable fuels is better.

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