Burning household waste

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SELCHP ("South East London Combined Heat and Power") [www.selchp. com] is a 35 MW power station that is paid to burn 420 kt per year of black-bag waste from the London area. They burn the waste as a whole, without sorting. After burning, ferrous metals are removed for recycling, hazardous wastes are filtered out and sent to a special landfill site, and the remaining ash is sent for reprocessing into recycled material for road building or construction use. The calorific value of the waste is 2.5kWh/kg, and the thermal efficiency of the power station is about 21%, so each 1 kg of waste gets turned into 0.5 kWh of electricity. The carbon emissions are about 1000 gCO2 per kWh. Of the 35 MW generated, about 4 MW is used by the plant itself to run its machinery and filtering processes.

Scaling this idea up, if every borough had one of these, and if everyone sent 1 kg per day of waste, then we'd get 0.5 kWh(e) per day per person from waste incineration.

This is similar to the figure estimated above for methane capture at landfill sites. And remember, we can't have both. More waste incineration means less methane gas leaking out of landfill sites. See figure 27.2, p206, and figure 27.3, p207, for further data on waste incineration.

Figure D.4. SELCHP - your trash is their business.

Notes and further reading page no.

283 The power per unit area of using willow, miscanthus, or poplar, for electricity is 0.2W/m2. Source: Select Committee on Science and Technology Minutes of Evidence - Memorandum from the Biotechnology & Biological Sciences Research Council [www.publications.parliament.uk/pa/ld200304/ ldselect/ldsctech/126/4032413. htm]. "Typically a sustainable crop of 10

dry t/ha/y of woody biomass can be produced in Northern Europe. ... Thus an area of 1 km2 will produce 1000 dry t/y - enough for a power output 150 kWe at low conversion efficiencies or 300 kWe at high conversion efficiencies." This means 0.15-0.3 W(e)/m2. See also Layzell et al. (2006), [3ap7lc].

283 Oilseed rape. Sources: Bayer Crop Science (2003), Evans (2007), www.defra. gov.uk.

- Sugarbeet. Source: statistics.defra.gov.uk/esg/default.asp

284 Bioethanol from corn. Source: Shapouri et al. (1995).

- Bioethanol from cellulose. See also Mabee et al. (2006).

- Jatropha. Sources: Francis et al. (2005), Asselbergs et al. (2006).

285 In America, in ponds fed with concentrated CO2, algae can grow at 30grams per square metre per day, producing 0.01 litres of biodiesel per square metre per day. Source: Putt (2007). This calculation has ignored the energy cost of running the algae ponds and processing the algae into biodiesel. Putt describes the energy balance of a proposed design for a 100-acre algae farm, powered by methane from an animal litter digester. The farm described would in fact produce less power than the methane power input. The 100-acre farm would use 2600 kW of methane, which corresponds to an input power density of 6.4 W/m2. To recap, the power density of the output, in the form of biodiesel, would be just 4.2 W/m2. All proposals to make biofuels should be approached with a critical eye!

286 A research study from the National Renewable Energy Laboratory predicted that genetically-modified green algae, covering an area of 11hectares, could produce 300 kg of hydrogen per day. Source: Amos (2004).

- Elean power station. Source: Government White Paper (2003). Elean Power Station (36 MW) - the UK's first straw-fired power plant. Straw production: www.biomassenergycentre.org.uk.

287 Landfill gas. Sources: Matthew Chester, City University, London, personal communication; Meadows (1996), Aitchison (1996); Alan Rosevear, UK Representative on Methane to Markets Landfill Gas Sub-Committee, May 2005 [4hamks].

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