An energetic life cycle assessment of C&D waste and container glass recycling in Cape Town,South Africa

This study presents the results of a comparative life cycle assessment (LCA) on the energy requirements and greenhouse gas (GHG) emission implications of recycling construction and demolition (C&D) rubble and container glass in Cape Town, South Africa. Cape Town is a medium sized city in a developing country with a growing population and a rising middle class, two factors that are resulting in increased generation of solid waste. The City is constrained in terms of landfill space and competing demands for municipal resources.The LCA assessment was based on locally gathered data, supplemented with ecoinvent life cycle inventory data modified to the local context. The results indicated that recycling container glass instead of landfilling can achieve an energy savings of 27% and a GHG emissions savings of 37%, with a net savings still being achieved even if collection practices are varied. The C&D waste results, however, showed net savings only for certain recycling strategies. Recycling C&D waste can avoid up to 90% of the energy and GHG emissions of landfilling when processed and reused onsite but, due to great dependence on haulage distances, a net reduction of energy use and GHG emissions could not be confidently discerned for offsite recycling. It was also found that recycling glass achieves significantly greater savings of energy and emissions than recycling an equivalent mass of C&D waste.The study demonstrated that LCA provides an important tool to inform decisions on supporting recycling activities where resources are limited. It also confirmed other researchers’ observations that strict adherence to the waste management hierarchy will not always result in the best environmental outcome, and that more nuanced analysis is required. The study found that the desirability of recycling from an energy and climate perspective cannot be predicted on the basis of whether such recycling conserves a non-renewable material. However, recycling that replaces a virgin product from an energy-intensive production process appears to be more robustly beneficial than recycling that replaces a product with little embodied energy. Particular caution is needed when applying the waste management hierarchy to the latter situations.     

The private and social economics of bulk electricity storage

The ability to store excess intermittent renewable electricity is increasingly being seen as a key option for integrating large quantities of renewable capacity. However, intermittent energy sources currently account for very small amounts of total generation. Despite this fact, policymakers have begun implementing requirements that will dramatically increase the amount of bulk storage capacity. This paper examines the social benefits provided by bulk storage in the Texas electricity market, which has a large amount of renewable capacity relative to other states, but still quite limited renewable penetration. We focus on the impact of arbitraging electricity across time—a major service of bulk storage. Using current storage technologies, we demonstrate that electricity arbitrage will increase daily CO₂ emissions by an average of 0.19 tons for each MWh stored. In addition, daily SO₂ emissions will increase by an average of 1.89 pounds/MWh while NO_X emissions will fall by an average of 0.15 pounds/MWh.     

Energy transformations in two tropical Oxbow lakes

The flow and pattern of energy utilization in two tropical ecosystems where polyculture of fishes was practiced were studied. The rates of organic production made by the two tropical natural aquatic systems (oxbow lakes) were studied for two annual cycles. The study of utilization of energy in two tropical lakes revealed that herbivores were more efficient in energy utilization than autotrophs. The energy available in these systems was supplied by allochthonous source. Silver carp and grass carp were found to be most efficient in conversion of energy in the grazing food chain of the lake. The efficiency of the system to fish production was found to be 0.06 (OL-I) ?0.05% (OL-II) of the total available solar radiation. Various forms of life are all accompanied by energy changes, in the studied lakes were found to form a food web.     

Long-term prediction model of rockburst in underground openings using heuristic algorithms and support vector machines

Rockburst possibility prediction is an important activity in many underground openings design and construction as well as mining production. Due to the complex features of rockburst hazard assessment systems, such as multivariables, strong coupling and strong interference, this study employs support vector machines (SVMs) for the determination of classification of long-term rockburst for underground openings. SVMs is firmly based on the theory of statistical learning algorithms, uses classification technique by introducing radial basis function (RBF) kernel function. The inputs of models are buried depth H, rocks’ maximum tangential stress σ_θ, rocks’ uniaxial compressive strength σ_c, rocks’ uniaxial tensile strength σ_t, stress coefficient σ_θ/σ_c, rock brittleness coefficient σ_c/σ_t and elastic energy index W_et. In order to improve predictive accuracy and generalization ability, the heuristic algorithms of genetic algorithm (GA) and particle swarm optimization algorithm (PSO) are adopted to automatically determine the optimal hyper-parameters for SVMs. The performance of hybrid models (GA + SVMs = GA-SVMs) and (PSO + SVMs = PSO-SVMs) have been compared with the grid search method of support vector machines (GSM-SVMs) model and the experimental values. It also gives variance of predicted data. A rockburst dataset, which consists of 132 samples, was employed to evaluate the current method for predicting rockburst grade, and the good results of overall success rate were obtained. The results indicated that the heuristic algorithms of GA and PSO can speed up SVMs parameter optimization search, the proposed method is robust model and might hold a high potential to become a useful tool in rockburst prediction research.     

Predicting national sustainability: The convergence of energetic,economic and environmental realities

The “constraint space” dictated by energetic, economic and environmental realities on scenarios for future organization of humanity and nature is explored from the perspective of the energy and resources driving economies. Net energy of energy sources is presented as an index (Emergy Yield Ratio; EYR) that must be evaluated for energy sources to better understand their potential contributions to society, but more important, as an indicator of the changes needed in the future if lower net yielding sources are to be relied upon. An aggregate EYR was calculated for the USA economy and shown to have decreased by 38% since 1950, from 11/1 to 6.8/1. Several measures of efficiency at the scale of national economies are explored and the data suggest that the most efficient economies are also the most energetically intense (as measured by empower intensity). An index of environmental loading is suggested as a measure to evaluate environmental efficacy. An obvious outcome is that the smallest most energetically intense countries have the highest environmental loads, and those with large land area and/or continental shelves have the lowest ratios. An Emergy Sustainability Index (EmSI) is defined, computed for countries, and proposed as a multi-dimensional measure of long-term sustainability. The most sustainable economies are those with the highest EYR and lowest environmental loads.     

Thermochemical stability: A comparison between experimental and predicted data

The first step to be performed during the development of a new industrial process should be the assessment of all hazards associated to the involved compounds. Particularly, the knowledge of all substances thermochemical parameters is a primary feature for such a hazard evaluation. CHETAH (CHEmical Thermodynamic And Hazard evaluation) is a prediction software suitable for calculating potential hazards of chemicals, mixtures or a single reaction that, using only the structure of the involved molecules and Benson's group contribution method, is able to calculate heats of formation, entropies, Gibbs free energies and reaction enthalpies. Because of its ability to predict the potential hazards of a material or mixture, CHETAH is part of the so-called “desktop methods” for early stage chemical safety analysis.In this work, CHETAH software has been used to compile a complete risk database reporting heats of decomposition and Energy Release Potential (ERP) for 342 common use chemicals. These compounds have been gathered into classes depending on their functional groups and similarities in their thermal behavior. Calculated decomposition enthalpies for each of the compounds have also been compared with experimental data obtained with either thermoanalytic or calorimetric techniques (Differential Scanning Calorimeter – DSC – and Accelerating Rate Calorimeter – ARC).     

Inherently safer sustained casing pressure testing for well integrity evaluation

This paper presents the use of a model to predict sustained casing pressure (SCP), from early pressure buildup data, as a basis for inherently safer well integrity testing. Inherently safer principles aim to eliminate or reduce the hazards by design rather than by using protective features. SCP, a well integrity issue exhibited in many wells, is any measurable pressure that rebuilds after being bled down and attributable to causes other than artificially applied pressure or temperature fluctuations in the well. Intrusion of gas, resulting in SCP, can occur because of poor cement bond in the casing or cement deterioration. Gas entering the annulus migrates to the wellhead and represents a hazard due to increased wellhead pressure and the gas inventory. Compromised well integrity can have catastrophic consequences on both environmental and safety aspects.Most regulations require the monitoring, testing and, eventually, the elimination of SCP. However, test data analysis is predominantly qualitative and limited to arbitrary criteria. Due to the high percentage of wells that present SCP, accurate, safe and preferably fast testing methods are needed. This paper implements an analytical model, rooted in the transport processes and thermodynamics of the system, to predict pressure profiles and gas accumulation during SCP testing from early-time pressure buildup data. The amount of gas accumulated during different testing criteria, being 1) current practices and 2) early diagnostic by the analytical model, is calculated and compared. Results show that using the analytical model as a predictive tool, testing time is reduced significantly, thereby limiting the amount of gas accumulated and reducing the risk. This makes the testing procedure inherently safer as well as less time consuming.     

PTA锻焊反应器的制造

本文对PTA装置上的大型铬钼钢锻焊反应器,在制造过程中的几个关键技术进行了介绍：控制材料的化学成分提高铬钼钢材料的抗回火脆化能力;采用先进的冶炼工艺和锻造技术保证大型锻件的质量;优化铬钼钢封头正火热处理中的冷却工艺来保证材料的性能指标;采用合理的焊接工艺,既保证了厚壁环焊缝的焊接质量,又降低了制造成本;优化堆焊工艺,保证了反应器内壁的堆焊质量;正确选择热处理规范,对铬钼钢压力容器至关重要。     

Are energy efficiency standards justified?

This paper develops an analytical framework for comparing the welfare effects of energy efficiency standards and pricing policies for reducing gasoline, electricity, and nationwide carbon emissions. The model is parameterized with US data and includes key externalities in the energy/transportation sectors and possible underinvestment in energy efficiency due to “misperceptions” over energy savings. Even with large misperceptions, the extra welfare gains from complementing efficient pricing policies with energy efficiency standards are zero for reducing gasoline and 5 percent for reducing electricity. And when viewed as substitutes, these standards forgo 60 percent or more of the potential welfare gains from corresponding pricing policies. A combination of energy efficiency and emissions standards is more than three times as costly as carbon pricing when there is no misperception over energy savings, and even with large misperceptions, combining carbon pricing with gasoline/electricity taxes is better than combining it with energy efficiency standards.     

生态建筑设计理论与实践研究

发展生态建筑已经成为当今社会发展的主题,同时也是顺应建筑全球化潮流,提升人居环境健康性和舒适性的迫切需要.必须不断转变建筑在设计和建设方面的思维方式,才能逐步缓解资源紧缺和环境污染的现状.该文对生态建筑定义以及设计原则两方面进行研究,通过对台湾水滴塔和新加坡展览塔楼这两座典型生态建筑案例进行了分析,再从生态建筑材料和生态建筑节能技术两方面予以阐述,得出生态建筑作为当今社会的发展趋势,其还有很多方面需要通过实践去探索.