Fbc For Waste Minimization

Due to low organic emissions levels, FBC is a promising technology for disposal of organic material-laden wastes. Donlee Technologies (USA) has developed a CFBC boiler to incinerate infectious hospital wastes by cofiring with coal [16]. Based on pilot-scale testing, they report that PAH, dioxin, and furan emissions were typically well below those achieved with other types of hospital waste incinerators. Furthermore, suppression of HC1 of up to 50% was achieved. Organic emissions met both the Pennsylvania Department of Environmental Resources and proposed California restrictions. FBC-based technology meeting all emission limits for PAH, dioxins, and furans has also been offered by Ogden Environmental Services (USA) for the successful destruction of a number of hazardous wastes, including PCB-contaminated soil [17,18],

FBC is being examined in Italy for the combustion of organic material-laden industrial, agricultural, and domestic wastes. Published results [19] indicate emission levels of dioxins and furans much lower than proposed European legislated limits. The potential of FBC technology as an inexpensive method for disposal of hazardous wastes is being examined in India by San-doz (India) and Thermax [20,21]. Thermax also reports that there are now 200 FBC installations operating in India burning a wide range of fuels from low grade coals to agrowastes such as rice hulls [21]. In India, FBC is overtaking rotary kilns as the preferred technology for the incineration of solid and liquid wastes [21],

The use of FBC (primarily bubbling bed technology) for incineration is strongly established in Japan [22,23]. FBC is routinely used to burn MSW, plastics, and tires among other materials (one supplier alone, EBARA Corp., has 40 FBC incinerators operating [23]). It has been reported that there are currently 113 FBC incinerators operating in Japan [24],

In Europe there are over 50 FBC incineration plants [25]. Studies have also shown that FBC can burn RDF and industrial waste plastics either directly or by cofiring with coal [26,27], A particularly interesting design concept, the fast internally circulating bed [25], used FBC technology to achieve "100%" elimination of all pollutants. The principal disadvantage of the concept was that the payback period in the Austrian context was inherently long, i.e., 15 years for a 10 MW(th) unit.

In North America, the use of bubbling fluidized bed combustion is increasingly finding more acceptance as a means for the production of energy from the combustion of used tires and municipal wastes [28]. In the United States, circulating fluidized bed combustion is being used for disposal of hazardous wastes [17,18]. In Canada, a 10 MW(e) revolving fluidized bed unit has recently been built to cleanly burn residues from tar ponds near Sydney, Nova Scotia [29]. Although the main thrust of this project is to clean up 700,000 tons of coke oven residues, the energy production is not unimportant. This unit is due to become fully operational in 1993.

Cofiring involves the burning of a waste "fuel" in conjunction with a premium fuel (coal, gas, or oil). Cofiring is used to supplement a waste fuel that may not be able to sustain combustion on its own or as a topping fuel if insufficient waste fuel is available. Cofiring, also known as "smart-burn," does not prevent recycling programs, as any reduction in the quantity of waste (particularly MSW) can be made up with the premium fuel. Cofiring thus appears to offer a palatable solution to the considerable municipal waste disposal problems now being experienced across North America. Traditional resistance to incinerators is likely to be reduced since as little or as much MSW can be burned or recycled as desired, based on local economic or legislative requirements.

Recently, the idea of cofiring coal and MSW or RDF has begun to find favor in the United States [30]. This is especially true in California, where the use of such wastes allows positive returns (extension of the lifetime of disposal sites; reduction in waste site emissions of green-

Table 1 Bubbling FBC Combustion of Biomass

Dry basis

Paper waste pellets

Alfa grass

Rice husks

Corn cobs

Wood pellets

% Volatiles

83.1

80.9

59.8

% Fixed C

15.2

14.6

13.4

% Sulfur

0.2

% Ash

1.6

4.4

22.2

HHV (MJ/kg)

18.1

18.8

14.1

Particle size

40-50 mm

3-cm fragments

< 10-mm husks

1-cm pieces

2-3-cm pieces

diam, 150-

mm-long

cylinders

Feed rate

40-80

61

20-70

70

80-90

(kg/hr)

Fluidization

0.9-1.2.4

2

0.4-2.2

1.4

1.3

velocity

(m/sec)

Combustion

>98%

96%

>97%

>96%

>90%

efficiency

CO

100-400 ppm

1.9%

>200 ppm (up

0.1-0.3%

0.6-1.0%

to 0.5 %)

NO, (ppm)

60-150

155

100-180

>450

60-80

S02 (ppm)

100-200

50-150

house gases and other toxic products; and generation of energy in the form of heat, process stream, and/or electricity) while still meeting the strict state environmental guidelines [31]. Elliot [31] quotes a figure of 3.6-4.1 cents/kWh for cofiring MSW compared with approximately 5.5 cents/kWh for a new coal-burning plant. Furthermore, these figures do not include a credit for the extension of the lifetime of the waste disposal facility or reduced liability costs for storage of potentially hazardous materials such as used tires. The economics of cofiring are therefore very favorable, findings that have been reinforced by a recent detailed literature survey on application of FBC to MSW [32]. In Canada, a number of companies are evaluating this technology and CANMET is also actively supporting FBC technology for biomass combustion [33,34],

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