Energy System Consequences When Installing an Advanced Delignification Process

In the pulp and paper industry, during major modernization projects the overall energy system consequences are often not estimated in detail, usually only local energy consequences are taken into account when evaluating possible projects. In this paper, the effects on the overall energy system when installing an advanced delignification process (i.e., a “state‐of‐the‐art” pulp digester and oxygen delignification process) will be presented. Also, the effect such an installation has on the potential for further energy integration is discussed. Furthermore, the CO₂ consequences for both installing such a system and integrating the mill further energy‐wise are presented.     

PAC-Bayesian Compression Bounds on the Prediction Error of Learning Algorithms for Classification

We consider bounds on the prediction error of classification algorithms based on sample compression. We refine the notion of a compression scheme to distinguish permutation and repetition invariant and non-permutation and repetition invariant compression schemes leading to different prediction error bounds. Also, we extend known results on compression to the case of non-zero empirical risk.We provide bounds on the prediction error of classifiers returned by mistake-driven online learning algorithms by interpreting mistake bounds as bounds on the size of the respective compression scheme of the algorithm. This leads to a bound on the prediction error of perceptron solutions that depends on the margin a support vector machine would achieve on the same training sample.Furthermore, using the property of compression we derive bounds on the average prediction error of kernel classifiers in the PAC-Bayesian framework. These bounds assume a prior measure over the expansion coefficients in the data-dependent kernel expansion and bound the average prediction error uniformly over subsets of the space of expansion coefficients.Editor Shai Ben-David     

Economy and CO2 emissions trade-off: A systematic approach for optimizing investments in process integration measures under uncertainty

In this paper we present a systematic approach for taking into account the resulting CO₂ emissions reductions from investments in process integration measures in industry when optimizing those investments under economic uncertainty. The fact that many of the uncertainties affecting investment decisions are related to future CO₂ emissions targets and policies implies that a method for optimizing not only economic criteria, but also greenhouse gas reductions, will provide better information to base the decisions on, and possibly also result in a more robust solution. In the proposed approach we apply a model for optimization of decisions on energy efficiency investments under uncertainty and regard the decision problem as a multiobjective programming problem. The method is applied to a case of energy efficiency investments at a chemical pulp mill. The case study is used to illustrate that the proposed method provides a good framework for decision-making about energy efficiency measures when considerations regarding greenhouse gas reductions influence the decisions. We show that by setting up the problem as a multiobjective programming model and at the same time incorporating uncertainties, the trade-off between economic and environmental criteria is clearly illustrated.     

Heat sources — technology, economy and environment

Heat sources for heat pumps in buildings as well as in industry are discussed. Furthermore, some environmental aspects concerning choice of heat source are highlighted. Only systems for heat pumping are included, i.e. air-conditioning types which can also partly work as heat pumps are excluded. Recent heat pump installations in Sweden are mainly in small systems. Ambient air, exhaust air, soil and rock are the most common heat source types. Data on COP, investment costs, working fluids, present Swedish market etc. for these types of heat sources are given. Data on industrial heat pump installations in some countries and distribution of these according to heat pump type and industry sector as well as heat source temperatures are reported. Process integration aspects when choosing heat source size and temperature are also discussed as well as the relation between these parameters and the choice of heat pump type. Finally, the influence on the economy of the heat source temperature is presented. The cost-effectiveness of heat pumps for reducing CO₂ emissions compared with other heating technologies is discussed. The main results are: (1) heat pumps can in many cases in the future contribute to a reduction of CO₂; (2) there is a rather big difference, for larger systems a major difference, between the water-based and the ambient air-based heat pumps in terms of efficient reduction of greenhouse gas emissions.     

Static and dynamic problem formulations for design optimization

This paper concerns an issue that may arise in design optimization of dynamical systems that possess multiple equilibrium points. If one considers only such points, it is possible to pose optimization problems in which the state problem is treated as a static problem. This is attractive as it reduces the computational cost compared to approaches which account for the entire state trajectory. However, if the system has multiple equilibria, it could happen that the equilibrium point attained when the system was optimized has only a small region of attraction. This means that in order to attain the desired state, the system must be initialized in its close vicinity, something which may be difficult in practise. In the paper we demonstrate this issue by considering design optimization of Neuro-Mechanical Shape Memory Devices (NMSMDs), a type of mechatronic systems that take on prescribed shapes when subjected to certain input stimuli introduced by the authors in an earlier paper. The conclusion is that although the static problem formulation considered has some attractive features, the existence of multiple equilibria for the governing equations of NMSMDs seems to necessitate the use of dynamic problem formulations.     

Topology optimization of periodic 3D heat transfer problems with 2D design

Structural and Multidisciplinary Optimization - We consider a model for density-based topology optimization (TO) of stationary heat transfer problems with design-dependent internal convection in 3D...     

Risk management in the oil industry: can information on long-run equilibrium prices be utilized?

We analyze co-movements between the prices of crude oil and major refined products during the period 1992–1998. Specifically, we explore the existence of long-run equilibrium price relationships, and whether deviations from estimated equilibrium can be utilized for predictions of short-term price changes and for risk management. The econometric evidence strongly supports the hypothesis that crude and product prices are co-integrated. Past deviations from long-term equilibrium are significant in an error correction specification of short-term product price changes. The results represent valuable information for hedging, particularly in integrated oil companies for which price risk is related to margin variations.     

Integration of algae-based biofuel production with an oil refinery: Energy and carbon footprint assessment

Biofuel production from algae feedstock has become a topic of interest in the recent decades since algae biomass cultivation is feasible in aquaculture and does therefore not compete with use of arable land. In the present work, hydrothermal liquefaction of both microalgae and macroalgae is evaluated for biofuel production and compared with transesterifying lipids extracted from microalgae as a benchmark process. The focus of the evaluation is on both the energy and carbon footprint performance of the processes. In addition, integration of the processes with an oil refinery has been assessed with regard to heat and material integration. It is shown that there are several potential benefits of co-locating an algae-based biorefinery at an oil refinery site and that the use of macroalgae as feedstock is more beneficial than the use of microalgae from a system energy performance perspective. Macroalgae-based hydrothermal liquefaction achieves the highest system energy efficiency of 38.6%, but has the lowest yield of liquid fuel (22.5 MJ per 100 MJ_algae) with a substantial amount of solid biochar produced (28.0 MJ per 100 MJ_algae). Microalgae-based hydrothermal liquefaction achieves the highest liquid biofuel yield (54.1 MJ per 100 MJ_algae), achieving a system efficiency of 30.6%. Macro-algae-based hydrothermal liquefaction achieves the highest CO₂ reduction potential, leading to savings of 24.5 resp 92 kt CO_2eq/year for the two future energy market scenarios considered, assuming a constant feedstock supply rate of 100 MW algae, generating 184.5, 177.1 and 229.6 GWh_biochar/year, respectively. Heat integration with the oil refinery is only possible to a limited extent for the hydrothermal liquefaction process routes, whereas the lipid extraction process can benefit to a larger extent from heat integration due to the lower temperature level of the process heat demand.     

Planning future investments in emerging energy technologies for pulp mills considering different scenarios for their investment cost development

In this paper, we propose a systematic approach to study how the development in terms of cost and proven functionality of emerging energy technologies affects the optimal choice and timing of investment decisions at an industrial plant today. The methodology used is based on stochastic programming, and all investments are optimized under uncertain energy market conditions. The cost development of the new technology is modeled using scenario analysis where both the cost levels and the timing of the market introduction are considered. Two examples are presented to illustrate the usefulness of the proposed approach. The examples are taken from the pulp and paper industry. In addition to investments in conventional technology for heat and/or power production, the emerging technology of carbon capture is considered as a possible future investment in the first example while lignin separation is considered in the second one. It is shown that possible future technologies can be highly important to consider already in today’s investment decisions.