Sustainability evaluation of decentralized electricity generation

Decentralized power generation is gaining significance in liberalized electricity markets. An increasing decentralization of power supply is expected to make a particular contribution to climate protection. This article investigates the advantages and disadvantages of decentralized electricity generation according to the overall concept of sustainable development. On the basis of a hierarchically structured set of sustainability criteria, four future scenarios for Germany are assessed, all of which describe different concepts of electricity supply in the context of the corresponding social and economic developments. The scenarios are developed in an explorative way according to the scenario method and the sustainability criteria are established by a discursive method with societal actors. The evaluation is carried out by scientific experts. By applying an expanded analytic hierarchy process (AHP), a multicriteria evaluation is conducted that identifies dissent among the experts. The results demonstrate that decentralized electricity generation can contribute to climate protection. The extent to which it simultaneously guarantees security of supply is still a matter of controversy. However, experts agree that technical and economic boundary conditions are of major importance in this field. In the final section, the article discusses the method employed here as well as implications for future decentralized energy supply.     

Acetylated and native corn starch blend films produced by blown extrusion

Thermoplastic starch (TPS) materials were developed from mixtures of native and acetylated corn starches with glycerol. To optimize the formulations an experimental design for multicomponent mixtures was used and the assayed formulations were determined by statistical software. Blends and pellets humidity content increased with glycerol concentration. Starch destructuration during the extrusion process was studied by thermal analysis. Films presented homogenous structure, rough surfaces and certain stickiness. They presented different properties, related mainly to the differential characteristics of native and acetylated starches and to hydrophilic character of glycerol. Their mechanical behavior indicated that they are a good option as a food packaging materials since TPS films resulted enough resistant to protect the product and flexible to resist moderate deformations. Besides, the use of acetylated starch in the formulations enhanced film resistance and reduced their WVP, despite of its low modification degree. The storage of the films under controlled conditions increased their stiffness, while their flexibility and WVP were reduced. Plasticizer migration towards the matrix surface was observed in stored films. Films resulted stable till a_w = 0.7 and due to their selective gaseous permeability they are useful to package products susceptible to oxidation or to control vegetable respiration and senescence.     

Integrated multi‐echelon supply chain design with inventories under uncertainty: MINLP models,computational strategies

We address in this article a problem that is of significance to the chemical industry, namely, the optimal design of a multi‐echelon supply chain and the associated inventory systems in the presence of uncertain customer demands. By using the guaranteed service approach to model the multi‐echelon stochastic inventory system, we develop an optimization model to simultaneously determine the transportation, inventory, and network structure of a multi‐echelon supply chain. The model is an MINLP with a nonconvex objective function including bilinear, trilinear, and square root terms. By exploiting the properties of the basic model, we reformulate this problem as a separable concave minimization program. A spatial decomposition algorithm based on the integration of Lagrangean relaxation and piecewise linear approximation is proposed to obtain near global optimal solutions with reasonable computational expense. Examples for specialty chemicals and industrial gas supply chains with up to 15 plants, 100 potential distribution centers, and 200 markets are presented. © 2009 American Institute of Chemical Engineers AIChE J, 2010