Suchergebnisse

The ancient peoples of the Southwest made use of a wide range of lithic and mineral resources, some of which were available locally to most communities, and others that could only be obtained through long- distance acquisition from limited and specific locations. The materials discussed here— clay, temper, and mineral pigments (including lead) used to make pottery, as well as tool stone, salt, and turquoise— range from those used for routine tasks on a daily basis to those more closely associated with ritual action. Their acquisition often required ritual preparation, prayers, and special trips to named places, many of which are part of the fabric of oral traditions and have shaped enduring cultural landscapes. For each of these materials, we briefly discuss their distribution, archaeological traces, analytical characterization, and means of sourcing. Tracing the movement of these resources across ancient landscapes has formed the basis of regional models of social, political, and economic interaction in Southwest archaeology. Pottery

China is under pressure to improve its agricultural productivity to keep up with the demands of a growing population with increasingly resource-intensive diets. This productivity improvement must occur against a backdrop of carbon intensity reduction targets, and a highly fragmented, nutrient-inefficient farming system. Moreover, the Chinese government increasingly recognizes the need to rationalize the management of the 800 million tonnes of agricultural crop straw that China produces each year, up to 40% of which is burned in-field as a waste. Biochar produced from these residues and applied to land could contribute to China's agricultural productivity, resource use efficiency and carbon reduction goals. However competing uses for China's straw residues are rapidly emerging, particularly from bioenergy generation. Therefore it is important to understand the relative economic viability and carbon abatement potential of directing agricultural residues to biochar rather than bioenergy. Using cost-benefit analysis (CBA) and life-cycle analysis (LCA), this paper therefore compares the economic viability and carbon abatement potential of biochar production via pyrolysis, with that of bioenergy production via briquetting and gasification. Straw reincorporation and in-field straw burning are used as baseline scenarios. We find that briquetting straw for heat energy is the most cost-effective carbon abatement technology, requiring a subsidy of $7 MgCO2e 1 abated. However China's current bioelectricity subsidy scheme makes gasification (NPV $12.6 million) more financially attractive for investors than both briquetting (NPV $7.34 million), and pyrolysis ($ 1.84 million). The direct carbon abatement potential of pyrolysis (1.06 MgCO2e per odt straw) is also lower than that of briquetting (1.35 MgCO2e per odt straw) and gasification (1.16 MgCO2e per odt straw). However indirect carbon abatement processes arising from biochar application could significantly improve the carbon abatement potential of the pyrolysis scenario. Likewise, increasing the agronomic value of biochar is essential for the pyrolysis scenario to compete as an economically viable, cost-effective mitigation technology.

China has developed ambitious bioenergy installation targets as part of its broader goals to increase its renewable energy generating capacity and decarbonise its economy. At present its main financial incentive to support bioenergy projects is a feed-in-tariff provided to units that generate electricity with 80% or more of their feedstock energy coming from agricultural residue biomass. Although this policy has catalysed the construction of many bioenergy units, there are reports that these projects are experiencing serious financial and technical problems, leading to low operational efficiency and even closure. An alternative option for China's agricultural residues is cofiring with coal in existing power stations. However this is currently unprofitable for power station operators, as cofiring is not eligible for financial assistance through the bioenergy feed-in-tariff. In light of China's ambitious target to install 30GW of bioenergy generation capacity by 2020, this paper investigates the extent to which extension of the bioenergy feed-in-tariff to include cofiring could contribute towards this goal. The results suggest that there is significant co-location of China's coal-fired powerstations and agricultural residues, with 39% of China's straw energy resources located within 50km of a power station. Assuming cofiring ratios of up to 10% coal energy replacement, the analysis finds that an annual 89-116TWh of electricity could be generated by cofiring agricultural residues collected within 50km radii of powerstations. If China extends its bioenergy subsidies to include cofiring, we estimate that an annual 72-100TWh can be produced at an internal rate of return of 8% or more. This equates to 48-67% of the bioenergy generation that China might expect if it were to meet its target of installing 30GW of bioenergy capacity. Overall this indicates a strong case for the Chinese government to extend its existing bioenergy feed-in-tariff to include cofiring at low energy replacement ratios.