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Ammonia production through more efficient technologies can be achieved using exergy analysis. Ammonia production is one of the most important but also one of most energy consuming processes in the chemical industry. Based on a panel of solutions previously developed, this study helps to identify potential areas of improvement using an exergy analysis that covers all aspects of conventional ammonia synthesis and separation. The total internal and external exergy losses are calculated as 3,152 and 6,364 kJ/kg, respectively. The process is then divided into five main functional blocks based on their exergy losses. The reforming block contains the largest exergy loss (3,098 kJ/kg) and thus the largest potential for improvement including preheating cold feed through an economizer, developing technology towards isobaric mixing, and pressure drop reduction in the secondary reformer as the main contributors to the irreversibility (1,302 kJ/kg) in this block. The second largest exergy loss resides in the ammonia synthesis block (3,075 kJ/kg) where solutions such as reduced temperature rise across the compressor, proper compressor isolation, reducing undesired components such as argon in the reactor feed, and using lower temperatures for reactor outlet streams, are proposed to decrease the exergy losses. Throttling process in the syngas separator is the key contributing mechanism for the irreversibility (1,635 kJ/kg exergy losses) in the gas upgrading block. The exergy losses in the residual ammonia removal block (833 kJ/kg exergy losses) are mainly due to the stripper and the absorber column where a modified column design might be helpful. The highest exergy loss in the preheating block belongs to the compressors (518 kJ/kg exergy losses) where a lower inlet temperature and better system isolation could help to reduce losses.

Abstract Anaerobic digestion of animal by-products was investigated in batch and semi-continuously fed, reactor experiments at 55 °C and for some experiments also at 37 °C. Separate or mixed by-products from pigs were tested. The methane potential measured by batch assays for meat- and bone flour, fat, blood, hair, meat, ribs, raw waste were: 225, 497, 487, 561, 582, 575, 359, 619 dm 3 kg −1 respectively, corresponding to 50–100% of the calculated theoretical methane potential. Dilution of the by-products had a positive effect on the specific methane yield with the highest dilutions giving the best results. High concentrations of long-chain fatty acids and ammonia in the by-products were found to inhibit the biogas process at concentrations higher than 5 g lipids dm −3 and 7 g N dm −3 respectively. Pretreatment (pasteurization: 70 °C, sterilization: 133 °C, and alkali hydrolysis (NaOH) had no effect on achieved methane yields. Mesophilic digestion was more stable than thermophilic digestion, and higher methane yield was noticed at high waste concentrations. The lower yield at thermophilic temperature and high waste concentration was due to ammonia inhibition. Co-digestion of 5% pork by-products mixed with pig manure at 37 °C showed 40% higher methane production compared to digestion of manure alone.

Ethylene oxide production process is one of the highest energy consumers in chemical industry, and therefore even a slight improvement in its overall efficiency can have a significant impact on the sustainability of the process. Efficiency improvement can be carried out using the exergy-aided pinch analysis outlined in this paper. The overall exergy loss distribution in different unit operations of an ethylene oxide process was first evaluated and mapped out in the form of “visualized exergetic process flowsheet”. An initial analysis of the four main functional blocks of the process showed that the exothermic reaction block contained the largest exergy loss (6043 and 428 kJ/kg of internal and external losses, respectively) which can be reduced by isothermal mixing, as well as increasing reaction temperature and reduction in pressure drop. The absorption block was also estimated to have the second highest contribution with total exergy losses of 3640 kJ/kg which were mainly due to the cooling column. These losses were then recommended to be reduced by improvements in the concentration and temperature gradients along the tower. Following the block-wise analysis, exergy analysis was then carried out for individual unit operations in each block to pinpoint the main sources of thermal exergetic inefficiency. Thermal solutions to reduce losses were also proposed in accordance with the identified sources of inefficiency, leading to a comprehensive list of cold and hot process streams that could be introduced to reduce losses. Finally, pinch analysis was brought into action to estimate the minimum energy requirements, to select utilities, and to design heat exchanger network. Thus, the methodology used in this work took advantage of both exergy and pinch analyses. The combined thermal-exergy-based pinch approach helped to set energy targets so that all the thermal possible solutions supported by exergy analysis were considered, preventing exclusion of any hot or cold process stream with high potential for heat integration during pinch analysis. Results indicated that the minimum cold utility requirement could be reduced from 601.64 MW (obtained via conventional pinch analysis) to 577.82 MW through screening of streams by the combined methodology.

This paper aims at reviewing the life cycle assessment (LCA) literature on second generation bioethanol based on lignocellulosic biomass and at identifying issues to be resolved for good LCA practice. Reviews are carried out on respective LCA studies published over the last six years. We use the classification of lignocellulosic biomass to define system boundaries, so that the comparison among LCA results can be thoroughly assessed based on identified system components. A basis for attributing environmental burden for different biomass feedstocks is also suggested. Despite the non-homogeneous systems, we conclude that second generation bioethanol performs better than fossil fuel at least for the two most studied impact categories, net energy output and global warming. For the latter category, carbon sequestration at the biomass generation stage can even consistently offset the GHG emissions from all parts of the life cycle chains at high ethanol percentage (≥85%). The aspect of biogenic carbon and agrochemical input for energy crops and biomass residues, and the effect of removal of the latter from soil have not been treated consistently. In contrast, the exclusion of upstream chain of biomass waste feedstocks is observed in practice. The bioethanol conversion process is mostly based on simultaneous saccharification and co-fermentation, characterized by high yield and low energy input. In this regard, the LCA results tend to under estimate the real impacts of the current technology. The choice of allocation methods strongly influences the final results, particularly when economic value is used as a reference. Substitution of avoided burden seems to be the most popular allocation method in practice, followed by partition based on mass, energy, and economic values.

A methodology for the sizing of domestic hot water heating and storage systems is defined, by assuming an extreme operating condition cycle composed of only two parts, a water consumption period and a system repositioning period. In both parts to respond to the extreme hot water demanding conditions, the heating is always on. The subsequent exergy analysis of this domestic hot water production system compares the irreversibility and the exergy efficiency of the water storage and the tankless situation. To carry out such analysis, some basic assumptions were made: a constant temperature heat source, a short duration operating cycle and a constant thermal energy supply. Under these circumstances it is shown that the hot water storage system leads to lower exergy losses while the tankless system is more exergy efficient, but requiring a higher instantaneous thermal power input. The use of the joule effect electricity, as the system heat source, be it a water storage one or a tankless one, maximizes the system irreversibility losses and minimizes the system exergy efficiency. The tankless system, with the joule effect electricity heat source is the worst situation.

ON 16 NOVEMBER 2000, the final report of the World Commission on Dams (WCD) was launched in London, in the presence of South Africa’s former president Nelson Mandela. This represented a remarkable milestone in the history of dam policy and politics. During its two-year existence, WCD had conducted the most extensive review of research and evidence regarding the planning, impacts, and management of large dams. It had engaged with numerous stakeholders around the globe. It also made comprehensive recommendations about how to improve dam planning and management.

Hot water heat stores with stratification are a common technology used in solar energy systems and reuse of waste heat. Adding a PCM module at the top of the water tank would give the system higher storage density, and compensate heat loss in the top layer. The work presented here includes experimental results and numerical simulation of the system using an explicit finite-difference method. Experiments and simulations were carried out using different cylindrical PCM modules. With only 1/16 of the volume of the store being PCM, 3/16 of water at the top of the store was held warm for 50% to 200% longer and the average energy density was increased by 20% to 45%. Furthermore, these 3/16 of water were reheated by the heat from the module after being cooled down in only 20 min.

Due to the increasing awareness of climate change, depletion of natural resources, and increasing world population, companies in the agri-food sector need to redesign their existing supply chains and take into account both the economic and environmental impact of their operations. In practice not all the required information is available in advance due to various sources of uncertainty in agri-food supply chains. In this research a multi-objective two-stage stochastic programming model is proposed to analyse and evaluate the economic and environmental impacts to account for uncertainty in agri-food supply chains. A mushroom supply chain in the Netherlands is presented as an illustrative case study. Optimal production planning decisions calculated with a two-stage stochastic programming model are compared with the results of an equivalent deterministic model. The results of the optimizations show that accounting for stochasticity in important model parameters can reduce the difference between expected and realized economic performance by approximately 4% on average. Moreover, this paper demonstrates that including stochastic model parameters can reduce the environmental impact without compromising the current economic performance. Given the assumptions in the setup of the case study and the available information, it is concluded that applying a 2-stage stochastic programming approach for production planning decisions can lead to improved economic and environmental performance in an agri-food supply chain. New findings in real-life case studies are needed to get profound insights and understanding on the impact of uncertainty on production planning decisions in sustainable agri-food supply chains.

European consumers are willing to pay more for “green” electricity, as they highly value renewable energy sources for the contribution to combating climate change. There is a push for getting higher levels of sustainability, leading to a differentiation of Europe‘s electricity market. In this differentiation, the large potential of wind energy is recognized. More specifically, North Sea countries prefer to plan wind arrays (far) out at sea. This article offers a review of the main arguments for offshore wind energy, described in comparison with its onshore counterpart. It is stated that offshore wind farms (OWFs) generate “dark green” electricity as they mitigate greenhouse gas emissions and contribute to the protection of (some) marine life. Applying an informational governance framework, this article further assesses whether this dark green message has been exploited through further differentiation of the electricity market, and provides an analysis of why this is not (yet) the case. It is concluded that the dominant discourse in onshore wind power development hinders a favorable ecological differentiation toward offshore wind power.