Global growth of traditional and novel thermal treatment technologies

Thermal treatment review

Global growth of traditional and novel thermal treatment technologies

by Nickolas J. Themelis

Thermal treatment facilities built in the 21st century have been based mostly on the grate combustion of ‘as received’ municipal solid waste (MSW). Three dominant technologies - those developed by Martin, Von Roll, Keppel-Seghers - have shown consistent growth of about three million metric tonnes of new waste-to-energy (WTE) capacity each year since 2000. In terms of novel technologies, direct smelting (JFE, Nippon Steel), fluidized bed (Ebara) and circulating fluidized bed (Zhejiang University) have accounted for an additional estimated growth of another one million tonnes per year.

Although some of the new processes are called ‘gasification’, in fact they are ‘gasification-combustion’ processes where the calorific value of the MSW is recovered in the form of steam (as in conventional WTE processes). The only true gasification process at an industrial scale is the Thermoselect process, currently operating at seven facilities built by JFE, a major Japanese steel maker.

This review examines the growth of dominant technologies and the emergence of novel solutions in the thermal treatment of waste. The global perspective on the current position of thermal treatment highlights how significant WTE is becoming worldwide. A look at thermal treatment technologies in China and Japan gives a sense of some of the novel solutions emerging in the market.

A global perspective

The Waste-To-Energy Research and Technology Council (WTERT), headquartered at Columbia University in New York City, keeps a close watch on the thermal treatment technologies used worldwide. In 2006, nominations were solicited for the 2006 WTERT Industrial Award to be presented to an operating WTE facility judged by an international committee to be among the best in the world on the basis of the following criteria:

• energy recovery in terms of kWh of electricity plus kWh of heat recovered per tonne of MSW, and as the percentage of thermal energy input in the MSW feed

• level of emissions achieved

• optimal resource recovery and beneficial use of WTE ash

• aesthetic appearance of the facility

• acceptance of the facility by the host community.

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From the nominations, 10 finalists were selected and requested to submit a specified set of 2005 operating data. The list of finalists included nine stoker grate (mass burn) facilities and one refuse-derived fuel (RDF) plant (Table 1).

The competition was fierce, as all 10 finalists had demonstrated high availability and very low emissions; Table 2 compares the emissions of the three top contenders for the award and gives the average emissions of all 10 plants, along with corresponding EU and US environmental standards. The WTERT 2006 Industry Award was won by the ASM Brescia facility which had the best combination of energy recovery, emissions and aesthetic appearance.

Greater capacity, lower emissions

Life-long opponents of waste-to-energy usually cite dioxin emissions as the main reason for their opposition. It is interesting to note that the 0.02 ng/nNm3 highlighted in Table 2 corresponds to an emission rate of 0.2 grams of dioxins per million tonnes of MSW combusted in these WTEs.

Opponents of combustion with energy recovery also claim that ‘incineration is dead’. Indeed a book of this title can be found on the internet. Of course, the term ‘incineration’ is too broad and should not be used to describe facilities that in fact are power plants using MSW as fuel. For example, in the USA there are over 1600 incinerators of all types but less than 300 units that combust MSW and recover energy.

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A recent review of the WTE industry by WTERT has shown that, since the beginning of this century, global capacity has increased steadily at the rate of about four million tonnes of MSW per year. This is illustrated in Table 3 (opposite), which summarizes the reported annual construction of new WTE capacity by only three technologies - Martin, Von Roll and Keppel-Seghers - at an average of 2.78 million tonnes per year. The contribution of all other technologies is estimated to about 1.2 million tonnes.

The ASM Brescia WTE plant, winner of the WTERT 2006 Industry Award

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China

The foremost university in China for the study of waste management is Zhejiang University where Professor Cen Kefa and his colleagues have developed the circulating fluidized bed (CFB) reactor used in several WTE facilities in China. According to estimates by the group at Zhejiang University, 668 cities in China landfilled 140-160 million tonnes of MSW in 2002 and the annual growth in MSW generation amounts to 6%-8%. These numbers suggest that as little as 187 million tonnes or high as 235 million tonnes of MSW could be landfilled in 2007. The accumulated amount of MSW in non-regulated landfills in China was estimated at 6 billion tonnes.

Total thermal treatment capacity in China is estimated at about 4 million tonnes in less than 50 facilities. About 4100 tonnes/day uses stoker grate technology - some provided from Europe (Martin, Alstom and Keppel Seghers) and some of domestic design.

The total installed capacity of Zhejiang University’s CFB technology is 3800 tonnes/day and another 3200 tonnes/day are under construction. The high efficiency of scavenging recyclable materials in China means that the calorific value of Chinese MSW can be as low as 5000 MJ/kg, i.e. half of that in the EU. For this reason, the Zhejiang CFB process mixes a small amount of coal with the MSW feed.

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It is interesting that, in a developing nation, a high cost technology such as the CFB process is gaining ground over landfilling. The two main reasons are the ability to recover indigenous energy and the scarcity of land in China for future landfills.

Japan

Japan is the largest user of thermal treatment of MSW in the world (40 million tonnes). The principal technology used is grate combustion of ‘as received MSW’ (i.e. mass burn). The major supplier is Mitsubishi Heavy Industries (using the Martin technology), followed by JFE.

However, there are over 100 thermal treatment plants using relatively novel processes such as direct smelting (JFE, Nippon Steel), the Ebara fluidization process and the Thermoselect gasification and melting technology process. These processes have emissions as low or lower than the conventional WTE combustion process, but produce a vitrified

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